>15yo 70% are supratentorial, <15yo 70% posterior fossa. 30% are metastases. Most of brain is neurons, but mature neurons do not divide, hence cannot be neoplastic; therefore gliomas most common tumours. Non-glial tumours are mostly extra-axial (coverings of brain or ventricular). Extra-axial tumours may invade intra-axially (eg aggressive meningioma, dural metastasis), intra-axial invading extra-axially is less common but may be seen in lymphoma, glioblastoma, metastases. Tumours are usually indolent, increased ICP, seizure or focal neurological defect, altered mental state (esp bifrontal tumour), altered equilibrium (cerebellar, CN8). Hydrocephalus causes HA, nausea/vomiting and papilloedema (partial obstruction of venous outflow optic nerve).
Usually hypodense with surrounding white matter oedema corresponding to biologic behaviour. Dark T1, bright T2. Tumoral haemorhage is often intermittent, thus mixed breakdown products (heterogeneous), blood-blood/fluid-blood levels in cystic/necrotic portions, delayed evolution. Tumours with higher vascularity and thus bleed include glioblastoma, melanoma, thyroid, RCC, oligodendroglioma, choriocarcinoma. T1 shortening seen with haemorrhage, fat (lipomas, dermoid), melanin (melanoma, similar to fat), calcification. Hyperdense and diffusion-restricting tumours are usually small cell eg lymphoma, pineoblastoma, neuroblastoma, medulloblastoma, melanoma, lung, colon, breast. Lower T2, from high nucleus:cytoplasmic ratio (thus less free water).
Enhancement (breakdown of BBB allowing macromolecular contrast to pass) in intra-axial tumour, inflammatory disease, subacute infarcts, postop gliosis, radiation necrosis. Enhancement also from new capillaries with intact BBB (esp low-grade neoplasms). Aggressive high-grade tumours have new leaky/fenestrated capillaries. Enhancement is not useful to caterogise low- or high- grade. Normal enhancement (no BBB) seen in the choroid plexus, pituitary, pineal glands, tuber cinerum and areas postrema (posterior medulla, controls vomiting and autonomic functions).
Ring-enhancing lesions ‘MAGIC DR’ – Metastases, Abscess (smooth, high T1/low T2), Gliobastoma, Infarct (subacute phase), Contusion, Demyelinating disease, Resolving haematoma/Radiation necrosis (M,A,G most common).
Marked surounding oedema seen with metastases, abscess, glioblastoma, radiation necrosis).
Congenital (<60days old) tumours – Teratoma (most common, 2/3 supratentorial), PNET (curvilinear sparse calcification), astrocytoma, choroid plexus papilloma, ependymoma, medulloepithelioma, germinoma, angioblastic meningioma, ganglioglioma.
Cerebellopontine angle masses ‘AMEN’:
- Acoustic/vestibular schwannoma – Low T1, high T2, enhances.
- Meningioma – Iso/low-T1, iso-high T2, enhances.
- Ependymoma – Low T1, high T2, enhances.
- Neuroepithelial cyst – Arachnoid, epidermoid cysts. Follows CSF, doesn’t enhance.
Posterior fossa tumours in adults most commonly metastasis then haemangioblastomas; in children:
- Pilocytic astrocytoma
- Brainstem glioma
- Atypical teratoid rhabdoid tumour (neonate)
Temporal lobe tumours:
- Low-grade astrocytoma
Sydromes at higher risk of brain tumours:
- Basal cell nevus syndrome (Gorlin syndrome) – Medulloblastoma. Dural calcification <10yo.
- Cowden disease
- Li-Fraumeni syndrome – Astrocytomas, PNET, choroid plexus tumours.
- Maffucci syndrome
- Ollier syndrome
- Tuberous sclerosis
- Turcot syndrome
The 2016 WHO classification is largely now based on genetic profile of tumours, which overrides histologicical classification. Tumours are thought to arise from proginator stem cells (located subventricular and in dentate gyrus of hippocampus). Divided based on founder mutation.
- IDH +ve (mutant) – Icocitrate dehydrogenase converts α-ketoglutarate (αKG) to 2-hydroxyglutarate (2HG). 2HG accumulates, is an oncometabolite, which may be seen on MRS at 2.25ppm (just before NAA), increased above 1mM (sensitivity 80%). 2HG will increase with progression, reduce with treatment. Best done at TE 97ms (to separate 2HG from Gln-Glu). Tumours tends to progress through stages over time. Commonly frontal lobes, large non-enhancing components. T2-FLAIR mismatch high specificity, high T2 with areas low FLAIR. IDH status does not change with time. IDH mutations do not occur <14-16yo (and is irrelevant)
- 1p19q codeletion (ATRX intact) – oligodendroglioma (WHO II), anaplastic oligodendroglioma (III)
- TP53 mutation and ATRX loss – diffuse astrocytoma (II), anaplastic astrocytoma (III), glioblastoma (IV)
- IDH -ve (wild type) – sporadic, primary GBM. IDH-wt tumours have worse prognosis than IDH-neg, even if it has a lower histological grade. Grade II/III IDH-wt tumours may not exist (even though may appear so on imaging/histology), can be termed molecular GBM. MGMT positive toomors have better prognosis (2-3yrs), commonly associated with pseudoprogression. MGMT-ve tumours worse prognosis (~1yr).
- BRAF – pilocytic astrocytoma PXA, eGBM, DNET, ganglioglioma. Good prognosis.
- H3 K27M – diffuse midline glioma (IV), diffuse intrinsic pontine glioma (DIPG). Children or young adults. All grade IV with poor prognosis, common leptomeningeal metastases. Seen mildline structures, thalamus, hypothalamus, pineal, spinal cord. Can haemorrhage.
- WNT – usually MCP
- Shh – usually lateral cerebellum
- Group 3
- Group 4 – usually diffuse, little/now enhancement
- Embryonal (ETMR) – no longer use the time PNET
- Ependymoma – 9 subgroups, all different
Immunohistochemistry assesses the affects of mutated genes, not the genes themselves. This is faster and cheaper than assessing genes directly. IDH1-R132H antibody detects IDH1, but misses the less common non-canonica IDH2 mutations.
Intra-Axial Gliomas (40-50%)
Astrocytes are the most common neuroglia, regulate chemical environment, anchor neurons to blood supply, predominant ‘building blocks’ of blood brain barrier. Oligodendrocytes insulate axons in the brain and spinal cord. Ependymal cells line cavities of CNS (blood-CNS barrier) and create CSF.
Graded on cellularity, mitotic activity, nuclear pleomorphism, necrosis, endothelial proliferation, and genetic markers. M slighlty > F. All lack a capsule. Spread via white matter tracts (corona radiata, corticospinal tract, corpus callosum, hippocampal commisures), perivascular/Virchow-Robin spaces, along subpial/subependymal surfaces or across meninges (rare). Infiltrating astrocytomas are >/= grade II.
Low grade (I-II) are slow growing, usually <40yo (peak 30-40yo). Often cystic but rarely haemorrhage, no necrosis/neovascularity. 20-25% calcify. Rarely surrounding oedema. Hypodense, low T1/high T2 (rarely no abnormal T2), <50% enhance. Frequently ill-defined, insinuating through neurons. In chidlren tend to occur along optic pathways, hypothalamus, near/in 3rd ventricle. Adults usually in cerebral hemispehres. 10% degenerate into higher grade tumours. Tx surgery ± chemotherapy, radiotherapy.
- Grade I (circumscribed) – Well circumscribed. Surgery usually curative. The posterior limit that a surgeon would usually excise a temporal tumour is usually the vein of Labbe.
- Juvenile pilocytic astrocytoma (JPA) – Most common infratentorial paediatric neoplasm. 60% in cerebellum, others in optic pathway, hypothalamus, 3rd ventricle (associated with hydrocephalus). Most <20yo, peak 9yo. Slow growing, several months HA, vomiting, gait disturbance, blurred vision, diplopia, neck pain. Associated with 20% of all NF1 patients, but usually in sites other than the cerebellum. 2/3 are cystic (younger patients) with enhancing mural nodule, cyst wall may enhance. 1/3 are solid masses (older patients, higher risk of anaplasia) ± necrotic centre. 20% calcify (usually solid). Haemorrhage rare. Well-defined iso/hypo-dense, iso/low-T1 and high T2, higher DWI/FLAIR than CSF (protein). Cystic portion contains proteinaceous fluid, fluid-fluid levels or wave pulsation artifact. Vasogenic oedema rare. Mural nodules shows intense enhancement and uptake on PET. DDx haemoangioblastoma (peak 35yo, mural nodule), infection (esp toxoplasmosis), other cystic gliomas. Excellent prognosis after resection.
- Subependymal giant cell astrocytoma (SEGA, SGCA) – 2-20yo, associated with tuberous sclerosis (rare without, seen in 10% of patients with TS). Typically near foramina of Monro projecting into ventricles (hydrocephalus), slow-growing, moderate to marked enhancement (cf tubers of TS), calcification. CECT more specific (subependymal nodules may enhance on MR but not on CT). Iso/hyper T1, high T2, some heterogeneity from calcification.
- Grade II (diffuse) – Poorly defined (may appear well-defined macroscopically), infiltrative expanding and distorting brain, but no necrosis or endothelial proliferation. May have cystic degeneration. 1/3 frontal lobe, 1/3 temporal lobes, commonly brainstem. Include fibrillary, geminocytic and protoplasmic astrocytomas. Will progress and de-differentiate over time. Cerebellar astrocytomas 85% are pilocytic, 15% fibrillary (infiltrative, solid, worse prognosis, older children). Germinocytic (rare) always cerebral hemispheres, most convert to glioblastomas. Monstrocellular (magnocelluar) and protoplasmic also rare.
- Pleomorphic xanthoastrocytoma (PXA) – <30yo (most <18yo). From subpial astrocytes esp peripheral temporal lobes (seizures). Heterogeneous cortical mass along meningocerebral interface, homogeneous enhancement, cystic in 1/3-1/2, well or poorly defined. Haemorrhage and calcification uncommon. DDx DNET.
- Brainstem glioma/astrocytoma – Usually WHO grade II or I. 80% childhood (3-10yo) of which they are 20% of posterior fossa masses. Patterns include intrinsic pontine gliomas (most, aggressive with poor prognosis), exophytic tumours from cervicomedullary junction (less aggressive) and tectal gliomas (more benign course). Infiltration through tracts with expansile enlargement of brainstem, cranial nerve palsies, pyramidal tract signs, ataxia. May also involve medulla, cervical cord. 20% exophytic, may shed cells into CSF. Altered 4th ventricle contour (flattened, displaced posteriorly or rotated). May extend through foramen magnum resembling ependymoma. Typically diffuse fibrillary type. 33% enhance, 25% cystic degeneration or haemorrhage. Calcification implies lower grade. Tumour infiltrates rather than destroyes (hence late symptoms), no hydrocephalus until late (slow growth), appears to encircle basilar artery. Expansion of brainstem DDx: lyphoma, rhombic encephalitis (Listeria), TB, demyelinating disease (ADEM, MS), infarction, resolving haematoma, vascular malformation. Tx chemotherapy and radiotherapy. 10-30% 5yr surival. Almost all recur within 2yrs.
High grade (III-IV) >40yo, poorly defined microscopically but may appear demarcated macroscopically, commonly necrosis/haemorrhage/neovascularity, odema. Heterogeneous, iso/low T1, high T2, ringlike enhancement. Astrocytomas in adult posterior fossa tend to be anaplastic astrocytoma or glioblastoma (cf JPA in children). Surrounding white matter T2 hyperintensity represents tumour cells amongst oedema, may be very subtle (‘fog’) and slowly extends along tracts over time.
- Grade III (anaplastic astrocytoma, AA) – Increasing cellularity/mitoses/pleomorphism. Most IDH wild type. Usually 30s-40s, ill-defined, extensive vasogenic oedema, enhancement. Any necrosis (eg haemorrage) is glioblastoma. Anaplasia in 75-80% with dedifferentiation into glioblastoma in 50% (average after 2yrs). Germistocytic astrocytmas have eosinophilic cell bodies. Usually treate with adjuvant radiotherapy and chemotherapy.
- Grade IV (glioblastoma, GBM) – Tumour cells de-differentiate into stem cells. Marked cellularity/mitoses/pleomorphism, extensive necrosis and endothelial proliferation. Tumour cells collect along the edges of necrotic regions with a pseudopalisading pattern. Most common (50-60% of astrocytomas, 15% of intracranial neoplasms), peak 45-55yo. 95% are IDH wild type (sporadic/primary, usually adults). Younger patients tend to have protracted Sx over years usually secondary to dedifferentiation of lower grade astrocytoma (IDH+). Most common deep white matter frontal lobe, parietal, then temporal lobe, basal ganglia. Expansile with central necrosis, 90% enhancement (solid, ring or mildly heterogeneous), extensive vasogenic oedema, heterogeneous, lobulated, haemorrhage on gradient, lactic acid on MRS. Ring enhancement = GBM, despite pathological findings (hence may need to re-biopsy). May have daughter/satellite peripheral lesions like cluster of grapes. Any surrounding high T2/FLAIR may be microscopic infiltration or oedema. Frequently crosses corpus callosum, anterior/posterior comissures. Occasional calcification. Increased relative cerebral blood volume (rCBV) indicates higher grade astrocytoma/glioblastoma, precedes development of enhancement. With increasing histological grade MRS demonstrates increasing Cho then reducing NAA then inverted lactate peak (necrosis). Subarachnoid seeding in 2-5%, may coat ventricles. Rapid progression with poor prognosis. Tx surgery, chemotherapy and radiotherapy. Recurrence within 1yr common, 3yr survival is 2%. Avastin (bevacizumab), a VEGF inhibitor will reduce T2 signal, enhancement and CBV due to direct effects of the drug; CBF may increase due to increasing flow of normal vessels.
- Giant cell glioblastoma (previously monstrocellular sarcoma) – <5% of all glioblastomas. Abundant multinucleated giant cells, fibrous network, more localised/demarcated tumour.
- Gliosarcoma – 2% of glioblastomas. Mesenchymal tumour, may be well-defined, superficial, strongly enhancing. May invade into skull/scalp.
- Butterfly glioma – Common spread through corpus callosum involving both frontal lobes. Abnormal signal in corpus callosum represents disease rather than oedema (fluid cannot be conducted through tightly packed callosal and internal capsule fibres). DDx lymphoma, infection, demyelinating disease.
- ‘Gliomatosis cerebri’ pattern (diagnosis no longer exists) – diffuse involvement of multiple regions of the brain. Almost all are IDH-wt.
Multicentric astrocytomas may be contiguous spread of tumour with inapparant connection (most) or true metachronous lesions (usually NF1).
Peak 30-50yo. Supratentorial in 85%, most frontal or temporal lobe, predilection for whtie matter but often extending to cortex, may erode calvarium. Slow-growing, always calcification on microscopy (70% on CT), 20% haemorrhage or cysts (higher risk of malignant astrocytoma), low T1, high T2. Network of anastomosing capillaries. Vasogenic oedema in 1/3. 66% variable enhancement. WHO grade II, but survival variably less at 38-75% 5yr.
- Anaplastic oligodendroglioma (WHO III) – Increasing cell density, anaplasia and necrosis, may be seen in nodoles within a grade II oligodendroglioma, may mimic glioblastoma and have worse prognosis.
- Mixed glioma – Combined with astrocyte elements eg oligoastrocytoma (similar appearance, less calcification, more enhancement, worse prognosis), and anaplastic oligoastrocytoma.
Diffuse Midline Glioma
Histone mutation H3K27M. Worst prognositc paediatic tumour. Mostly brainstem gliomas.
WHO grade II. Mostly children/adolescents, usually <10yo, second peak 30s-40s. From ependymal cells lining ventricles (children, typically near 4th ventricle) or central canal of spinal cord (adults). Spinal ependymomas associated with NF2. Perivascular pseudorosettes with tumour cells around vessels. Supratentorial tends to arise intra-axially, large and cystic. Soft and pliable. Insidious increase in intraventricular pressure. In 4th ventricle typically solid/papillary masses from the floor (cf medulloblastoma roof), extending through foramina of Luschka or Magendie (characteristic, but DDx choroid plexus papilloma). Hypo/iso-dense, heterogeneous with calcification (50%, typically punctate), small cysts (15%) and haemorrhage (10%). Iso/low T1, intermediate/high T2. Heterogeneous patchy mild enhancement. Hydrocephalus common. Subarachnoid seeding common. Total resection from 4th ventricle is difficult. 5-yr survival 60% (best -> worst: filum terminale, spinal cord, supratentorial, posterior fossa). Anaplastic ependymomas are WHO III, with increased density/mitoses/necroses, poor prognosis (worse when younger), rapid growth, commonly enhances.
- Myxopapillary ependymomas – Occur in filum terminale, papillary elements in myxoid background.
From thin glial layer under ependyma of ventricles, containing subependymal neuroglia. WHO grade I. Resembles ependymomas, usually present late adulthood (>40yo). Intraventricular or periventricular esp lateral recess 4th ventricle’ (50%), lateral ventricles attaching to septum pellucidum (45%), occasionally spinal. Well-circumscribed lobulated intraventricular mass, isodense, iso/low T1, high T2. Most don’t enhance. Larger tumours may have cysts, calcification, haemorrhage.
(Primitive neuroectodermal tumour PNET, poorly differentiated neoplasms). WHO grade IV tumours.
Most <10yo (50% of paediatric posterior fossa tumours), peaks 4-8yo and 15-35yo. M>F. <3/12 of HA, vomiting, truncal ataxia. WHO grade IV with rapid growth. 85% from cerebellar vermis. In older children/adults tends to be more lateral extraventricular (thought to arise from undifferentiated bipontential percursors in cerebellar midline which migrate laterally with age) and more agressive, less well-defined. Commonly extends into superior/inferior velum of 4th ventricle displacing it anteroinferiorly with hydrocephalus (cf ependymoma enlarging ventricle while maintaining shape). Most are solid, slightly hyperdense (cf astrocytoma hypodense), homogeneous, usually well-defined, mild/moderate vasogenic oedema. Necrosis or cystic change in 10-20% paediatric and 60-80% of adults. Calcification in 10-20%. Haemorrhage uncommon. Iso/hypo T1, variable T2 (variable nuclear-cytoplastmic ratio). Blurring of cerebellar folia best seen on midline sagittal (infiltration), may involve leptomeninges. Intense heterogeneous enhancement. Cerebellopontine angle involvement is rare. Elevated choline, low NAA/Cho (higher in astrocytomas, ependymomas), low Cr/Cho (higher in ependymomas), lactate not usually present (often in astrocytomas, ependymomas). Tend to aggregate beneath the pia, penetrate and cause CSF spread (33% at time of diagnosis) with sugar-coating or nodular metastases in ventricles, thecal sac (hence should image entire spinal axis). Systemic metastases in 5%, most commonly bone. Tx surgical resection, chemotherapy, radiotherapy.
Desmoplastic medulloblastoma – Rare variant, may arise extra-axially esp CP angle.
Supratentorial Primitive Neuroectodermal Tumour (S-PNET)
(Previously cerebral neuroblastoma, ganglioneuroblastoma if ganglion cells present). Mean 5yo (most <10yo), M>F. ?From bipotential precursor cells of germinal matrix (-> glial or neuronal cells). Large (30-100mm) well-defined heterogeneous solid-cystic mass in deep white matter, commonly periventricular/intraventricular. Hydrocephalus common. Calcification in 50-70%. Necrosis and haemorrhage common. Variable vasogenic oedema. Hyperdense, low T1, iso/high T2, enhance. WHO grade IV. High rate of recurrence and subarachnoid seeding. Prognosis 34% at 5yr, worse with younger age.
Infants, supratentorial > infratentorial, temporal > parietal. Commonly cysts, calcification, haemorrhage, necrosis, enhancement. Rapid progression, subarachnoid seeding. WHO grade IV.
From periventricular neuroepithelial precursor cells. Neonates and young children. Usually supratentorial, large, enhance, oedema, peripheral necrosis and cysts, relatively well-circumscribed. Invades leptomeninges, adjacent to ventricles. CSF dissemination. WHO grade IV.
Atypical Teratoid/Rhabdoid Tumour (ATRT)
Highly malignant, WHO grade IV. Neonate, almost all <5yo. 50% posterior fossa, 40% supratentorial, others peripineal, multifocal, intraspinal. Rhabdoid cells with eosinophilic cytoplasm, mimic rhabdomyosarcoma. Large, hyperdense, heterogeneous, haemorrhage, necrosis, calcification, cyst, patchy enhancement. Spread along surface of brain, common subarachnoid spread. Prognosis <1yr.
Neuronal and Mixed Neuronal/Glial Tumours
Most <30yo. Mixed astrocytic glial and neuronal ganglion cells. Low grade, good prognosis. Long-standing focal seizures, hypothalamic dysfunction. F>M. Most temporal lobe (85%), frontal lobe, anterior 3rd ventricle, cerebellum, occasionally spinal cord, optic nerves. Slow-growing with bony remodeling. Hypo/iso-dense, 50% cystic (± mural nodule, may simulate arachnoid cyst), 1/3 calcify, 50% faint enhancement. <10yo are larger and more cystic with solid enhancing components. Higher grade (defined by glial portion) predicted by uptake of FDG or Th-201, vasogenic oedema. May convert to anaplastic ganglioglioma.
Desmoplastic Infantile Ganglioglioma (DIG)
Variant of ganglioglioma with very large heterogeneous mass. Almost always <2yo, M:F 2:1. Rapidly expanding head. Usually frontal and parietal lobes. Large peripheral cystic and solid mass with solid desmoplastic tissue along meningocerebral interface with intense enhancement, adherent to dura. May have calcified rim. WHO grade I, good prognosis. DDx DNET and PNET.
Desmoplastic Infantile Astrocytoma
(Desmoplastic cerebral astrocytoma of infancy). ?Variant of DIG with glial and mesenchymal cells, but no neuronal cells. <2yo. Benign form of astrocytoma. Usually supratentorial, dural-based, cystic, enhancing mass (no enhancement of cyst, even rim). Rarely mass effect or vasogenic oedema.
Purely neuronal cells. No glial component, hence no potential for malignant degeneration. Usually cerebral cortex or cerebellum (Lhermitte-Duclos disease). May be hyperdense, little/no enhancement, iso T1 and T2, high FLAIR.
(Dysplastic cerebellar gangliocytoma, diffuse ganglioneuroma, Purkinjeoma, diffuse hypertrophy, ganule cell hypertrophy). ?Hamartoma. Early 20s. 1/2 associated with Cowden disaese. CT often N. ‘Striated’ cerebellar infiltrative mass involving white and grey matter, high T2 with minimal vasogenic oedema, no enhancement. WHO grade I.
Dysembryoplastic Neuroepithelial/Neuroectodermal Tumour (DNT/DNET)
Rare, most 10-30yo with medically refractory seizures, neurological deficits uncommon. WHO grade I. Most temporal and frontal lobes, occasionally septum pellucidum. Peripheral involving cortex and subcortical white matter (wedge-shaped abnormal). Hypodense. Soap bubble appearance with cysts, septations, ‘floating neurons’ in pools of mucopolysaccharide-rich fluid. Exophytic extension beyond normal grey matter margin ± pressure erosion of skull. Calcification in 5%. Variable enhancement. Usually no vasogenic odema. May have adjacent focal cortical dysplasias (in 50%) or low grade astrocytoma. Excellent prognosis even with only partial resection. DDx ganglioglioma.
WHO grade II. From septum pellucidum or lateral/3rd veinticular wall. Most 20-40yo. 50% lateral ventricle near foramen of Monro, 20% involve 3rd ventricle. 10% bilateral. Histology similar to oligodendroglioma. Well-circumscribed, lobulated, hyperdense ± cystic change and calcifications, isointense to grey matter on all MR sequences. Swiss cheese morphology – numerous cystic lesions. Intense and diffuse enhancement with prominent vascular flow voids. Haemorrhage common, rarely vasogenic oedema. DDx oligodendroglioma.
Extraventricular neurocytomas are rare, in deep white matter, hemispheric grey matter. Large, well-defined, variable enhancement, cystic, haemorrhagic, calcified.
Other Intra-Axial Tumours
Rare, unknown origin. Young adults, cerebral hemispheres. Well-defined, peripheral enhancement, central necrosis, large. Variably aggressive but good prognosis with resection.
Benign (WHO grade I), most young/middle-aged. 25% associated with vHL, when they are often multiple. Most in cerebellar hemispheres (most common intra-axial adult infratentorial tumour), spinal cord (esp cervical), medulla, rarely cerebral hemispheres. Usually abuts a pial surface. No capsule, hence recurrence common. Well-defined cystic mass, intense enhancing pial mural nodule (in 60%) receiving blood from pia (cyst >> nodule cf JPA). Prominent adjacent vessels that extend into the nodule. Nontumoural cyst (non-enhancing cyst wall). 40% are atypical with solid enhancemnet (esp vermis). Calcification rare. May see serpiginous flow voids in nodule. Tx resection of nodule only, good prognosis. DDx JPA (younger, nodule larger and hypovascular), meningioma.
Primary CNS Lymphoma (PCNSL)
(Diffuse histocytic lymphoma, reticulum cell sarcoma, microglioma, primary cerebral lymphoma). Almost always B-cell NHL. Increasing incidence due to increasing immunocompromised patients (latently infected by EBV), where they are the most common CNS neoplasm. Increased risk with MS. Confusion, lethargy, memory loss. Small blue cells with high nucleus-to-cytoplasm ratio, packed in perivascular spaces. Hyperdense (may be hypodense in AIDS), lower T2, vasogenic oedema. Usually multifocal in deep grey matter or white matter, periventricular spread or along leptomeninges. Enhancement in almost all (may not in AIDS). 85% supratentorial, 10% cerebellum. Increased necrosis and multifocality in immunocompromised. Bright on DWI. Calcification and haemorrhage rare. Common subependymal spread and bihemispheric involvement (‘butterfly glioma’ pattern). Very sensitive to steroids and radiotherapy with aggressive rebound (ghost tumour); poor response to chemotherapy (cf peripheral lymphomas). Best to avoid steroids until biopsy. Thallium avid (cf toxoplasmosis). Variable CBV depending on grade (toxoplasmosis hypovascular). DDx toxoplasmosis (tends to be at grey-white interface or basal ganglia, ring enhancement, doesn’t abut ependymal surface), metastases, focal cerebritis.
Intravascular lymphomatosis (angiotropic/angiocentral lymphoma) – Intraluminal growth within small vessels, involving brain and often other regions of body. May cause occlusions with small vessel infarcts, linear enhancement or diffusion restriction. Poor prognosis.
Secondary lymphoma usually involves leptomeninges, nerve roots and CSF, difficult to detect on imaging. May have hydrocephalus. Dural invasion rare. May have parenchymal extension.
Multinodular and Vacuolated Ganglion Cell Tumour (MVNT)
Uncertain if this is neoplastic or hamartomatous. Benign, do not progress with time, no followup required. Unique appearances. Cluster of small cysts under the cortex at the depth of a sulcus. Doesn’t suppress with FLAIR. No enhancement. Almost always incidental asymptomatic, minority associated with seizures.
Choroid Plexus Tumours
- Meningioma – Esp atrium.
- Metastases – Lung, RCC.
- Choroid plexus papilloma and carcinoma
- Haemangioma (Sturge-Weber)
Choroid Plexus Papilloma and Carcinoma
Common in children (most <5yo) esp trigone lateral ventricle, in adults usually in 4th ventricle; carcinomas usually in lateral ventricles. May cause hydrocephalus from increased CSF production of the tumour (4-5x N) or obstruction (tumour, haemorrhage, high protein or adhesions). Choroid plexus papillomas are WHO grade 1; the rarer carcinomas are grade II (almost all in young children, if adults likely metastatic carcinoma). Well-defined, typically hyperdense, multilobulated mulberry appearance, engulfs the glomus of choroid plexus, iso/low T1, mixed high T2, marked enhancement. Calcification in 20-25%, (choroid plexus calcification <10yo is abnormal’). Heterogeneity or parenchymal invasion suggests carcinoma. CSF seeding in 60%. DDx primary melanoma of the choroid plexus.
Choroid Plexus Haemangioma
Benign, usually lateral ventricle. Marked enhancement, may calcify, usually incidental. May be associated with Sturge-Weber ipsilateral to meningeal lesion.
Choroid Plexus Xanthogranuloma
Benign, incidental, may have fat density, centered on glomus of trigone. Frequently bright on DWI.
(Neuroendodermal/paraphyseal cyst). Not a true neoplasm. Anterosuperior 3rd ventricle near foramen of Monro, causes acute hydrocephalus from osbtruction. Acute severe headache reproducible by tilting head forward (Brun phenomenon). Some are entirely cystic with gelatinous/proteinaceous material; others heterogeneous with old haemorrhage, cholesterol crystals, various ions. May have dot sign (low T2 signal), which may fill the cyst. Lined by simple to pseudostratified epithelium ?respiratory epithelial origin. Variable appearance, most hyperdense (protein), faint rim enhancement in 40%. Important to describe relation to internal cerebral veins for surgical approach.
Congenital, non-neoplastic, lined by epithelium ?from ectoderm. Usually within ependyma of ventricles (esp lateral) centered on choroid plexus, occasionally spinal canal, parenchyma, extra-axial intracranial space. May be associated with previous infection or hemorrhage in ventricles. Follows CSF except may be bright T1 due to cholesterol, protein, mucin or viscous content.
Abnormal proliferation of normal brain tissue in abnormal location. Propensity for hypothalamus, presenting with precocious puberty, visual disturbance, seizures, gelastic seizures (laughing spells). Other locations include cerebral cortex-subcortical region, periventricular. Isointense to grey matter on T1, variable T2.
Fetus in fetu – Duplication of brain structures, usualy extra-axial frontal mass. May have ectopic brain in nasopharynx, patienterygopalatine fossa.
1/3 of intracranial neoplasms. 80% grey-white interface, 3% basal ganglia, 15% cerebellum. Intra-axial from lung, breast, melanoma, colon, RCC, thyroid. Extra-axial dural from breast, lymphoma, prostate (almost neve invades brain), lung, neuroblastoma. Silent metastases in small cell carcinoma, lung (esp adenocarcinoma), melanoma. 80-85% supratentorial except RCC (posterior fossa). 50% solitary (esp breast, uterine, GI). 10% haemorrhagic (esp melanoma, RCC, thyroid, choriocarcinoma, retinoblastoma), but since lung and breast more common this is seen more. Cystic or calcified in lung, breast, GI. Multiple lesions at grey-white interface, hypodense, low T1/variable T2, marked vasogenic oedema (except cortically based lesions where there is less interstitium), intense ring or nodular enhancement. More well-defined than gliomas. Melanomas have high T1 and iso/low T2 due to paramagnetic melanin (unless nonhaemorrhagic amelanotic melanoma). Lesions better detected with increased contrast, 30min delay, 3T MR, magnetisation transfer suppression to post-T1 (suppresses high protein background).
Leptomeningeal carcinomatosis – Spread by primary CNS malignancies, extracranial adenocarcinoma (esp lung, breast), leukaemia or lymphoma. Commonly involves basal cisterns, cranial nerve palsies, hydrocephalus. DDx meningitis. Best seen with posterior fat sat or FLAIR.
Skull lesions may be obscured with contrast T1. Best seen with fat sat T2. MR best for epidural and intracranial extension, CT for subtle bony erosion.
Paraneoplastic syndromes associated with antibodies (anti-Yo, anti-Hu, anti-Ma, anti-Ri, anti-CAR, anti-Ta/Ma2). Treatment of primary tumour usually improves symptoms.
- Limbic encephalitis – Temporal lobe abnormality with memory and mental status change. Usually bilateral, extensive high T2 ± enhancement ± atrophy, similar to herpes encephalitis. Haemorrhage rare. From small cell lung cancer, testicular germ cell, thymic, ovarian, breast, haematologic and GI cancers.
- Cerebellar atrophy with ataxia from ovarian carcinoma, lymphoma.
Most malignant tumours are from bone metastases with aggressive bony abnormality, involves inner and outer table, extraosseous soft tissue, multiple.
F:M 2:1 intracranial, 10:1 intraspinal. Peak age 50-60yo. Hormonally sensitive, may grow more rapidly during pregnancy. Multiple tumours associated with NF2 in 9%, rare in children without NF. Most benign, slow-growing. 90% supratentorial. Arise from arachnoid meningothelial cell, usually attached to the dura. Location parasagittal or convexity (50%), sphenoid wing (20%), CP angle, olfactory groove, parasellar (10%) or ventricles (most common in children), tentorium, optic nerve sheath. 2-3% intraspinal esp thoracic spine. 1% extra-CNS/extra-dural esp sinonasal, parotid, deep tissues, skin; from arachnoid cell rests (dural fibroblasts and pial cells). 15 subtypes including meningothelial, fibrous/fibroblastic, transitional/mixed, psammomatous, angiomatous, microcystic, secretory, lymphoplasmacyte-rich, metaplastic, clear cell (WHO II), chordoid (WHO II), atypical (WHO II), papillary (WHO III), rhabdoid (WHO III), anaplastic (malignant, WHO III). Globular or en plauqe shapes.
Hyperdense in 60%. Variable oedema from compressive ischaemia, venous stasis, aggressive growth or parasitisation of pial vessels. Adjacent inner table hyperostosis (esp if en plaque) or osteolysis in 40%, esp skull base or anterior cranial fossa (not seen in schwannomas); ?from tumour infiltration of marrow space or hypervascular periosteum. Prominent dural grooves from enlarged middle meningeal arteries. Calcification in 20%. Rarely cystic, osteoblastic, chondromatous, fatty degeneration or haemorrhage. May extend into IAM. On MR iso/low T1, iso/low T2, heterogeneous from cysts/vessels/calcification, may have hypointense rim, prominent pial vessel flow voids in 80%, cleft sign in 80% (interposed CSF, hypointense dura or blood vessels). High T2 tumour signal may be due to microcystic or chordoid variant. Adjacent dural thickening/tail in 60-70% which is usually reactive fibrovascular proliferation rather than neoplastic invasion (non-specific, but more common than other diagnoses eg schwannoma). May encase and narrow adjacent vessels (cf pituitary adenomas which don’t). Reduction in calibre of dural sinus is suspicious for involvement, confirmed with MRA or conventional angiography. Intense homogeneous enhancement with arterial phase radial vessels (spoke-wheel, often from a bony spur) with early dense blush persisting into venous phase (mother-in-law sign), enlarged dural vessels ± AV shunting. Supplied by middle meningeal artery (ECA), anterior meningeal (ophthalmic) or posterior meningeal (veretebral). Vasogenic oedema within adjacent brain due to VEGF secretion of the meningioma. Rarely invade brain, increasing risk of recurrence but doesn’t alter WHO grade. On MRS high alanine and absent NAA, no glutamine. Tx resection ± preoperative embolisation (esp skull base). Embolisation may cause tumour infarction with rapid increase in swelling/mass effect. DDx sarcoid, plasmacytoma, lymphoma, dural metastases. Rarely a metastasis may deposit in a meningioma (collision tumour).
- Atypical meningioma (2.4%) – WHO grade II with increased mitotic rate, high nucleus/cytoplasm ratio, prominent nucleoli, sheet-like growth and necrotic foci. More restricted diffusion, otherwise appear like typical benign meningioma. More frequently recurs, may require radiotherapy.
- Malignant/anaplastic meningioma (1%) – WHO grade III with multiple mitoses or sarcomatous degeneration, rapid growth, intraparenchymal invasion, restricted diffusion. Papillary meningiomas undergo malignant degeneration more commonly than others.
- Radiation-induced meningioma – Radiation induced meningiomas are 5x more common than gliomas or sarcomas. Appears in radiation field decades later, multiple in 30%. Faster rate of growth, higher rate of atypia/anaplasia and recurrence.
(Previously angioblastic meningioma). Rare, 30-50yo, M>F. From modified pericapillary smooth muscle (pericytes of Zimmerman). Agressive, high recurrence, late metastases. Similar to meningioma. Tends to be large (>40mm), supratentorial, narrow dural base, multilobulated, heterogeneous, hyperdense, enhance, bony destruction more common. Calcification and hyperostosis uncommon.
Rare. Intra- and extra-axial involving cortex (90%) or meninges. Slow-growth, calcification, proliferating small vessels and fibroblasts, cysts. Most associated with NF2.
Peripheral Nerve Sheath Tumours (PNST)
Oligodentrocytes transition to Schwann cells within several mm of brain substance.
(Neurilemmoma, neurinoma). From Schwann cells that form myelin sheaths of axons. Loss of expression of NF2 gene (chromosome 22) product merlin, may be associated with NF2. Focal, encapsulated, can be separated from the nerve. Cranial nerves esp vestibulocochlear (VIII), trigeminal (V), and facial (VII); less commonly CNIX-CNXI. Seen at spine, foramen magnum, foram ovale, foramen rotundum, orbit, cerebellopontine angle, cavernous sinus, suprasellar region. Antoni A tissue has densely packed fibrous and neural tissue and Verocay bodies, causing darker T2. Antoni B tissue is looser myxomatous tissue with brighter T2. Subtypes include cellular, plexiform and melanotic (50% have Carney complex with facial pigmentation, cardiac myxomas, endocrine disorder eg Cushing/acromegaly/pheochromocytoma/adrenal hyperplasia; >10% become malignant). Malignant schwannoma more common with NF1. Arachnoid/peritumour cysts in 7-10% (esp larger tumours).
Best seen on thin-section (<3mm) axial and coronal T1. Usually iso/hypo-dense (cf meningioma hyperdense), don’t usually calcify. Low T1, high T2 (higher than meningiomas). Intense homogeneous enhancement. Cystic degeneration common esp if large (cf fatty degeneration in meningioma). Haemorrhage in 5% with susceptibility (esp vestibular schwannoma). Doesn’t tend to have dural tail or vascular flow voids (cf meningioma). Spectroscopy will show elevated myoinositol peak. Widening of neural foramen, orbital fissure or IAM. Oblong/dumbell-shaped.
- Vestibular schwannoma – Vestibular division of CN8 (incorrectly termed acoustic neuroma) in internal auditory canal, causes ipsilateral sensorineural hearing loss. Usually intracanalicular and cisternal portions. Expansion of canal with flared porus acousticus (on CT >2mm asymmetry of IACs). Bilateral in NF2. DDx cerebellopontine meningioma (rarely enhancement extending down CN7/8 cf 80% of schwannomas, but may have dural tail), intracanalicular lipoma (differentiated by fat-sat images), epidermoid, schwannoma from other cranial nerves.
- Trigeminal schwannoma – Pontine cistern at midpons level, between trigeminal ganglion (Meckel cave posterolateral to cavernous sinus) and brainstem. May extend through ganglion into foramen ovale, foramen rotundum or superior orbital fissure. Causes burning facial pain.
- Jugular schwannoma – More commonly grows intracranially into posterior fossa than extracranial. Smooth erosion of jugular foramen with sclerotic border (cf paraganglioma), compression of jugular vein (cf paraganglioma invading). Usually presents with hearing loss and vertigo.
Contain fibroblasts, perineural cells and Schwann cells. Each fascicle of the nerve is infiltrated by the neoplasm, hence impossible to separate. Cranial nerve neurofibromas are uncommon, spinal nerve rare. Rarely cystic or haemorrhagic. Rarely solitary, more common in NF1 (not usually NF2).
- Cutaneous/solitary neurofibroma – Localised masses in dermis/subcutaneous tissues, often have overlying hyperpigmentation. Highly collagenised with little myxoid material.
- Plexiform neurofibroma – Grow in and expand anywhere along a peripheral nerve, usually large nerve trunks. Frequently multiple. Predominantly myxoid tissue. May cause neurologic deficits and have malignant potential. Target sign on T2 with low central and high peripheral signal.
Posttraumatic proliferation of nerve cells (not a true neoplasm). Usually C-spine after nerve avulsion. Similar appearances to small schwannomas.
Malignant Peripheral Nerve Sheath Tumours (MPNST)
Highly malignant and invasive. Mostly medium to large nerves. 50% in NF1, from transformed plexiform neurofibroma or after radiotherapy.
Rarely CNS, in intradural extramedullary cervicothoracic spine. Congenital cyst ?failed cleavage between endodermal bronchial/GIT and spinal system. Lined by endodermal cells, may have persistent connection (canal of Kovalesky), may have coexisting thoracic bronchoenteric cyst. Typically bright/variable T1 (protein), bright T2, doesn’t enhance. May cause bony remodeling. Most associated with vertebral segementation abnormality (hemivertebra, block vertebra, Klippel-Feil, butterfly vertebra, fused vertebra).
From ectoderm persisting within infolded neural placode, may or may not communicate with skin as dermal sinus tract (in spine). Epidermal inclusion cyst of desquamated skin (keratin, cholesterin) lined by stratified squamous epithelium; not a neoplasm, slow-growing. Pearly appearance. M=F, 20-50yo, more common than dermoid. Most off midline in CP angle (may cuase trigeminal neuralgia, facial paralysis), suprasellar cistern, prepontine cistern, pineal region. Intradural 9x more common than extradural (may arise in diploic space, petrous bone, temporal bone with sclerotic borders). Low density (slightly higher than CSF), expands to fill interstices of CSF, tightly adherent to, and compressing adjacent structures, scalloped borders, lobulated, doesn’t enhance (unless previous surgery or infection, may have rim enhancement from granulation tissue), calcification in 25%, follows close to CSF intensity (bright T2, dark T1) except bright on FLAIR and DWI, rarely bright on T1 (high protein or cholesterol). DDx arachnoid cyst. In spine most common T5-8, may be intradural or extradural or both.
From ectoderm persisting within infolded neural placode, may or may not communicate with skin as dermal sinus tract (in spine). Dermal inclusion cyst with skin appendages/pilosebaceous unit (hair follices, sebaceous cysts); not a true neoplasm, slow-growing. M>F, 20-30yo, favours midline (cf epidermoids off midline) in inferior vermis, vallecula. May cause hydrocephalus, chemical meningitis (if ruptured), infection (if associated with sinus tract). Fat density/intensity with suppression on fat-sat (represents sebum rather than fat), heterogeneous with calcification and soft tissue, fat-fluid level (pathognomonic), doesn’t enhance (unless infected), chemical shift artifact. Rupture -> scattered fat particles, lipid in CSF. May have sinus tract in nasofrontal or occipital regions. In spine most common T5-8, may be intradural or extradural or both.
True congenital neoplasm of multipotential germ cells containing ectodermal (skin, brain), mesodermal (cartilage, bone, fat, muscle) and endodermal (cysts with aerodigestive mucosa) elements. Commonly pineal and suprasellar. Mixed density/intensity, enhancing nodule, may have peripheral enhancement if previous surgery/infection.
Congenital CSF collection within layers of arachnoid. ‘Secondary’/’acquired’ arachnoid cysts are actually leptomeningeal cysts from previous inflamamtory process. True arachnoid cysts from secretion of CSF from lining of cyst. May be symptomatic or assymptomatic. 50% are in middle cranial fossa, others at parasellar cisterns, frontal convexity, retrocerebellar cistern, CP angle cistern, quadrigeminal plate cistern. Intraventricular cysts rare, favour lateral and 3rd ventricles. If large, may obstruct CSF. Follows CSF signal on all sequences (occasionally higher on PD/FLAIR/DWI due to stasis of fluid cf pulsatile CSF); rarely may contain higher protein content. May distort adjacent pareynchyma, temporal lobe hypoplasia, bone remodeling. Inward displacement of cortical vessels. No enhancement unless infected. No restriction on DWI (cf epidermoids). No or delayed filling on cisternography (cf mega cisterna magna). DDx subdural hygroma, dilated subarachnoid space (underlying atrophy/encephalomalacia), epidermoid cyst. If a suprasellar cyst with hydrocephalus is shunted then may this may change the cyst morphology and subsequently compress optic chiasm causing blindness; thus the importance or recognising – fine slice T2 may be needed to visualise cyst membrane.
Osseous (osteoma, osteosarcoma), chondroid (chondroma, chondrosarcoma), muscular (leiomyoma, rhabdomyosarcoma), fatty (lipoma, liposarcoma) or fibrous (fibroma, fibrosarcoma).
- Lipoma – Congenital choristoma (normal tissue in abnormal site), not true neoplasm. ?From incomplete resorption of meninx primitiva as it develops into subarachnoid space. Associated with agenesis of the corpus callosum (if in interhemispheric falx may prevent formation), congenital abnormality of neural elements. Usually assymptomatic, incidental. Most pericallosal, quadrigeminal plate cistern, suprasellar, CP angle. Pericallosal lipomas may be curvilinear (thin along CC) or tubulonodular (ill-defined borders, surrounding calc, nodules extending into ventricles via callosal dysgenesis). Fat density/intesity, doesn’t enhance, chemical shift artifact, occasionally calcifies, may have blood vessel or cranial nerve traversing through (excluding dermoid).
- CNS sarcomas – Usually along meninges (meningosarcoma, angiosarcoma, fibrosarcoma), frequently invading the brain.
- Chloroma (granulocytic sarcoma). Tumour of immature granulocytes with myelogenous leukemia. May be anywhere, may predate onset of leukemia. In CNS typically orbit and epidural space, occasionally dura, intra-axial.
- Choristoma – Mass of normal tissue in aberrant location with smoth muscle and fibrous tissue, may be hypervascular. Usually extra-axial inclduing sella, parasella, IAM.
- Diffuse melanocytosis – Children, usually posterior fossa mass, high T1. May have spread through Virchow-Robin spaces.
- Melanocytoma (most common) – Adults.
- Neurocutaneous melanosis – Melanocytic nevi of skin (esp face), syringomyelia, CNS lipomas. Poor prognosis.
- Malignant melanoma – May haemorrhage, spread from dura to adjacent nerves/brain/skull.
- Skull lesions (breast, lung, prostate, RCC) may cause epidural metastases. Subdural metastases ?from haematogenous spread. Spinal lesions spread from a pelvic primary via Batson venous plexus. Typically biconvex, adjacent skull involvement.
- Dural metastases usually haematogenous from breast, lymphoma, lung, prostate, melanoma. In children neuroblastoma and leukemia (lodging in cranial sutures causing widening). Multiple en plaque lesions. Some from adjacent bone metastasis. DDx meningioma, sarcoidosis, plasmacytoma, lymphoma, granulomatous infections (mycobacteria, syphilis, fungal), Erdheim-Chester disease, LCH.
- Secondary CNS lymphoma – Rare, more commonly affects leptomeninges. Difficult to destinguish from meningioma. Almost always enhances (unless on high dose steroids).
- Subarachnoid seeding – Usually tiny diffuse tiny nodules (sugar-coating), may have focal nodules. From primary CNS tumour (glioblastoma, CNS lymphoma, oligodendroglioma, PNET, medulloblastoma, ependymoma, pineal tumours, retinoblastoma, choroid plexus papilloma), lymphoma, leukemia, or metastases (breast, lung, melanoma, neuroblastoma, GI/GU). Bright subarachnoid spaces on FLAIR (malignant cells or elevated protein), best seen on Gad FLAIR. Typically basal cisterns, interpeduncular cistern, CP angle, along cranial nerves, convexities. May cause hydrocephalus. Meningeal carcinomatosis – multiple cranial neuropathies/radiculopathies, meningeal irritation and hydrocephalus. Might only be detected on multiple CSF taps. DDx arachnoiditis, Gulillain-Barre, sarcoidosis, infectious granulomatous meningitis, Lyme disease, CMV radiculitis.
Pineal Region Masses
Pineal gland contains pineocytes (photosensory and neuroendocrine functions) in a neuroglial stroma, occasional sequestered embryonic germ cells. Secreted melatonin controls circadian rhythms. 60% are germ cell tumours (germinoma, teratoma, embryonal carcinoma, endodermal sinus tumour, choriocarcinoma), 15% pineal parenchymal tumours (pineocytoma, pineoblastoma), others include pineal cyst, glioma, meningioma (tentorium), arachnoid cyst, vein of Galen malformationm, lipoma. Germinomas (M>>F) unable to to differentiate from pineal parenchymal tumour (F>M) radiologically. Pineal gland grows until 2yo then stabilises; calcification is pathological when <6yo or >10mm. Masses may cause hydrocephalus (obstructed aqueduct), precocious puberty, paresis of upward gaze (Parinaud syndrome from compression of superior colliculus).
Germ Cell Tumours
Well-defined, usually midline, 65% in pineal region. Most <20yo. More common in Japanese. ?Rests of germ cells the remain in the CNS or migrate from other sites. Germ cell tumour metastases to the CNS are not uncommon, hence other origin should be sought. Elevated AFP in embryonal cell carcinoma, teratoma or choriocarcinoma. Elevated HCG in choriocarcinoma.
- Germinoma (most common) – In pineal (M>>F) or suprasellar (F>M) regions; occasionally basal ganglia, thalami. Most commonly children and young adults, peak age puberty. More common in Asians. Histologically similar to testicular seminoma and ovarian dysgerminoma. Iso/hyper-dense, well-circumscribed. Engulges normal physiologic calcification (cf exploded calcification in pineal parenchymal tumour), intermediate/low T1, low T2 (high nucleus/cytoplasmic ratio, cf pineal parenchymal tumour), intense enhancement. May have cystic degeneration and calcification. CSF dissemination common. Sensitive to radiotherapy and chemotherapy.
- Teratoma – Younger age group than germinomas. Variable appearance and behaviour. Most common pineal region, also in 3rd ventricle, posterior fossa. Exteremely heterogeneous containing all 3 germ cell lines (fat, calcification, cysts). Hydrocephalus common. Variable enhancement.
- Embryonal carcinoma, choriocarcinoma and endodermal sinus tumour – Highly malignant, frequently haemorrhagic. No specific radiological features. Choriocarcinoma positive for HCG and human placental lactogen.
Pineal Parenchymal Tumours
- Pineoblastoma – Highly aggressive, WHO grade IV. Histologically and radiologically similar to medulloblastoma, ?PNET. <30yo, most young chidlren. Ill-defined with lobular contour, local invasion, frequent calcification. Haemorrhage rare. CSF spread common (as with other PNETs). Rarely associated with bilateral retinoblastomas (trilateral retinoblastoma, mutation in RB). Iso/hyper-dense, iso/hypo-T1, variable T2, intense enhancement. May ‘explode’ the pineal gland calcification peripherally.
- Pineocytoma – Most common adults. Usually well-defined, noninvasive, slow-growing, calcification common, smaller (<30mm). Rarely metastasizes. Unable to differentiate from germinoma or pineoblastoma. Iso/hyper-dense, iso/hypo-T1, variable T2, intense enhancement. WHO grade II.
- Pineal Cyst – Common (40% on autopsy), signal follows CSF, but lack of CSF pulsation means slightly higher T1 and T2. No enhancement or internal architecture. May be eccentric to the gland, DDx small pineal neoplasm. Slight flattening of superior colliculus, but doesn’t tend to cause Parinaud syndrome or hydrocephalus. May be round/oval, can be >20mm. Those >10mm should be followed up. Intracystic haemorrhage rare. Usually lacks growth on followup (cf cystic astrocytoma). ?Form late childhood and regress in late adulthood. Occasionally may have peripheral calcification or enhancement, fluid-fluid levels, haemorrhagic mass effect, growth with time.
- Gliomas – From glial stroma of gland. Often low grade. May be indistinguishable from glial reaction accompanying pineal cysts.
Patients should have MR within 48-72hrs after surgery as baseline. Granulation tissue takes ~48-72h to fully develop, enhances, usually thin and linear becoming thicker and nodular, persisting for weeks-months. Enhancement <72hrs is likely residual tumour. Any intraparenchymal enhancement and mass effect after 1yr is suspicious. Dural enhancement almost always seen at 1yr, may persist for decades.
On followup of gliomas seizures has a high suspicion of tumour progression, even if imaging may be stable.
Pseudoprogression may show increased T2 signal and enhancement then later improving (over months-years). Patient remains clinically well cf true progression.
Effects of radiotherapy:
- Early (weeks or during therapy) – Transient white matter oedema.
- Early delayed (<3 months) – Also transient.
- Late delayed (>3 months) – Usually irreversible affecting white > grey matter with vascular changes including coagulative necrosis, hyalinisation. May be focal or diffuse. In 10%, 70% within 2yrs.
- Radiation necrosis favours primary tumour site (?predisposing vascular effects), difficult to destinguish from recurrent tumour. Residual/recurrent tumour is usually FDG PET (or Th-201) avid (cf low in radiation necrosis, better accuracy with higher grade tumours), elevated choline, increased CBV. Dynamic contrast enhancement shows gradual enhancement/uptake over time compared to rapid enhancement then plateau.
- Severe demyelination is diffuse esp periventricular and posterior centrum semiovale, usually doesn’t enhance.
- Meneralising microangiopathy (?intimal injury) causes calcification of basal ganglia or dentate nuclei, rarely cerebral cortex with associated atrophy. Usually >6 months, children > adults.
- Radiation vasculitis with focal narrowings.
- Telangiectasias, cavernomas and other cerebrovascular malformations, seen on T2*.
- Disseminated necrotising leukoencephalopathy – Severe radiation injury, usually in conjunction with chemotherapy.