Pituitary and Parasellar Region

The pituitary has maximum height of 9mm women, 8mm men, 6mm <12yo, upper surface flat of slightly concave. May increase in size up to 12mm from pysiological hypertrophy in puberty, pregnancy, lactation. The gland gradually reduces in size after 50yo. Anterior lobe iso T1 and T2, higher T1 in infants and pregnancy. Posterior lobe is high T1 (normal pituitary bright spot), low T2. The anterior lobe (adenohypohysis, 80% of the gland) develops from Rathke’s pouch, a deverticulum of primitive buccal cavity (stomodeum) which extends though sphenoidal septum and vomer as the craniopharyngeal canal, closing in early infancy. The posterior lobe (neurohypophysis) develops from neuroectoderm migrating from the hypothalamus. The hypothalamus controls the adenohypophysis via releasing hormones through the portal vessels; all are excitary excepit dopamine inhibitory on prolactin, growth hormone has stimulatory and inhibitory influences. Cells in the adenohypophysis include:

  • Somatotrophs (50%) produce growth hormone (GH)
  • Lactotrophs (mammotrophs) produce prolactin
  • Corticotrophs produce aderenocorticotropic hormone (ACTH), pro-opiomelanocortin (POMC), melanocyte-stimulating hormone (MSH), endorphins and lipotropin
  • Thyrotrophs produce thyroid-stimulating hormone (TSH)
  • Gonadotrophs produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Hyperpituitarism is from adenomas, hyperplasia or carcinomas of the adenyhypophysis; or secretion by nonpituitary tumours. Compression of optic chiasm and infundibulum also cause hypothalamic dysfunction (emotional disturbance, diabetes insipidus, precocious puberty) and visual changes (typically bitemporal hemianopsia). Suprasellar masses ‘SATCHMO’: Sella/pituitary tumour, Sarcoid, Aneurysm, Arachnoid cyst, Teratoma, Craniopharyngioma, Hypothalamic glioma, Hamartoma of tuber cinereum, Histiocytosis, Meningioma, Optic nerve glioma.

Sella

Pituitary Adenoma

5x more common than craniopharyngiomas or Rathke cleft cysts, prevalence 14% (most incidentaloma microadenomas). Peak 35-60yo. Microadenomas are </=10mm, macroadenomas >10mm. Functional (75%, typically microadenomas) or nonfunctional (typically macroadenomas, may cause hypopituitarism). Some adenomas can secrete 2 hormones (esp GH and prolactin), rarely more.

Typically lateral adenomas:

  • Prolactinoma (lactoroph adenoma, 30%) – Amenorrhoea, glactorrhoea, impotence, infertility. Commonly dystrophic calcification which may encompass almost the whole tumour (‘pituitary stone’). Prolactinaemia tends to correlate with te size of the adenoma. Serum prolactin >150ng/mL almost always indicates prolactinoma, >1,000ng/mL indicates invasion into cavernous sinus (normal <20ng/mL). Hyperprolactinaemia may also occur in normal pregnancy (peaks at delivery), lactation, stress, interference to dopamine inhibition (injury to hypothalamus, pituitary stalk, drugs, suprasellar mass). Tx surgery or bromocriptine (dopamine agonist).
  • GH-secreting (somatotroph adenoma) – GH stimulates hepatic secretion of insulin-like growth factor 1 (IGF-1) causing acromegaly, giantism (before physeal closure). Acromegaly causes skin and soft tissue thickening, hyperostosis of spine and hips, enlarged jaw (prognathism), enlarged hands and feet with broad digits. May be large at presentation).

Typically central adenomas:

  • ACTH (corticotroph) adenoma – Hypercortisolism with Cushing disease. Usually small at presentation. Nelson syndrome – ACTH adenoma post-excision of adrenal gland tumour due to loss of inhibitory corticosteroids on a pre-existing microadenoma, present with mass effect or hyperpigmentation.
  • Gonadotroph (FSH and LH) adenoma – Inefficient and variable secretion of hormones, usually non-functioning. Typically present in middle age with mass effect from macroadenoma, or hypopituitarism esp LH (reduced energy, amenorrhea).
  • TSH (Thyrotroph) adenoma – Rare, hyperthyroidism.

Best seen on coronal images as focal hypodense, low T1 (but may be iso- or hyper-). On dynamic imaging hypointence on immediate postcontrast (within 1st minute), hyperintence on delayed (~30min). Deviation of infundibulum, asymmetric convexity of the pituitary, mild downsloping of roof of sphenoid sinus, eroded sella turcica and anterior clinoid process. May have cystic components if large. A pituitary mass is most likely an adenoma if normal pituitary cannot be seen separately. Invasive adenomas may spread into the cavernous sinus with extension lateral to the lateral wall of cavernous ICA, obliteration of the carotid sulcus venous compartment (inferomedial to basal turn cavernous ICA) or >50% ICA encasement; indeterminate if extends between midpoint and lateral wall of ICA. Does not cause ICA narrowing (cf meningioma). Macroadenomas may haemorrhage (rapid expansion may cause pituitary apoplexy or be assymptomatic) or infarct (may be cystic similar to craniopharyngioma or Rathke cyst), may cause optic chiasm compression, CN palsy, hydrocephalus, anterior pit dysfunction. Generally iso-T1, cause ‘draping’ of optic chiasm over the top of the tumour. Intracranial ectopic pituitary adenoma usually suprasellar cistern, continuous with the pituitary stalk from cells of the pars tuberalis.

Pituitary Apoplexy

Clinical syndrome¬†of sudden ophthalmoplegia, HA, visual loss or vomiting. From pituitary infarction or haemorrhage, usually associated with an adenoma. Pituitary haemorrhage doesn’t cause haemosiderin deposition. Sheehan syndrome is postpartum pituitary ischaemic necrosis, from physiological enlargement outstripping vascular demand. May have fluid-level. Pituitary haemorrhage may be assymptomatic (in which case it is not apoplexy).

Lymphocytic Hypophysitis

F:M 9:1, often post-partum or 3rd trimester. Mostly affects the anterior pituitary (lymphocytic adenohypophysitis LAH), mimics adenoma but faster growing; rarely posterior (lymphocytic infundibular neurohypophysitis LINH) causing diabetes insipidus. Infiltration of lymphocytes, similar to orbital pseudotumour and Tolosa-Hunt. May have perisellar reduced T2 signal (developing over weeks) from fibrosis in adjacent cavernous sinus. Ill-defined borders, may erode bone without remodelling. Usually self-limiting.

Empty Sella Syndrome

Enlarged empty sella turcica. May be associated with visual field defects, hyperprolactinaemia, hypopituitism. May see herniation of chiasm and 3rd ventricle into the sella from adhesions. Primary is from defect in diaphragma sella allowing arachnoid and CSF to herniate compressing the pituitary (aging or pseudotumour cerebri). Secondary is from infarction, surgery or radiotherapy.

Hypopituitarism

When ~75% of parenchyma is lost. From tumour (adenoma, mets, Rathke cleft cyst), trauma and SAH (common), surgery/radiation, apoplexy, ischaemia (Sheehan syndrome), empty sella syndrome, congenital, hypothalamic lesion, inflammation or infection (sarcoidosis, TB). If hypopituitarism is accompanied by neurohypophysis dysfunction (diabetes insipidus), it implies an hypothalamic origin. Most of those with isolated hormone deficiency have thin/truncated infundibulum, normal or small adenohypophysis. Those with mutliple hormonal deficiencies usually have small/absent adenohypophysis or stalk and ectopic or absent neurohypophysis bright spot. Pituitary dwarfism occurs in children from reduced growth hormone.

Posterior Pituitary Syndromes

The neurohypophysis contains pituicytes (modified glial cells) with axons extending from hypothalamis via pituitary stalk; produces oxytocin and antidiuretic hormone (ADH, vasopressin). These are synthesized in the hyopthalamus and stored in axon terminals of the posterior pituitary.

  • Central diabetes insipidus – Polyuria from ADH deficiency (cf nephrogenic from unresponsive renal tubules). From head trauma, tumours, inflammation, surgery or spontaneous.
  • Syndrome of inappropriate ADH (SIADH) secretion – Hyponatraemia. Most from ectopic ADH secretion by cancers (esp SCLC), drugs, CNS infection or trauma.

Other Pituitary Lesions

  • Pituitary carcinoma – Rare, defined by craniospinal or systemic metastases. Most are functional, most commonly prolactin or ACTH.
  • Metastases – Include breast, GIT, lymphoma. May cause oedema within the brain (cf adenomas), tend to enhance more than adenomas. Faster growing than adenoma, with ill-defined border, may erode through bone without associated remodelling.
  • Granulomatous disease – Giant cell granuloma, LCH, sarcoidosis. May cause hypopituitarism, diabetes insipidus.
  • Ipilimumab induced hypophysitis – targeted chemotherapy esp for melanoma. Usually develops 6-12 weeks after starting treatment. Panhypopituitism.
  • Pituicytoma (choristoma, granular cell tumour, myoblastoma of the posterior pituitary) – Rare, from pituicytes in neurohypophysis. Variable T1, PD and T2, enhances. Localised to the posterior pituitary.
  • Meningioma – Most from diaphragma sella. May have dural tail, ICA narrowing, homogeneous enhancement.
  • Intrasellar ICA aneurysms.
  • Persistent trigeminal artery – May pass through sella from ICA to basilar a.
  • Deposition in haemochromatosis, amyloidosis, Hurler syndrome.
  • Spontaneous intracranial hypotension – May cause pituitary enlargement. Also see enhancing dura, enlarged venous plexus of C-spine, tonsillar herniation.

Suprasellar

Craniopharyngioma

From metaplastic squamous epithelial remnants of Rathke pouch at the anterior pituitary and infundibulum. Larger than Rathke cleft cyst, frequently symptomatic. Most common paediatric suprasellar mass, peak 5-10yo with second peak 50-60yo. Typically 30-40mm. 70% involve intra- and supra-sellar compartments, 20% purely suprasella, 10% sella. May extend into anterior/middle/posterior fossa, retroclival, lateral ventrilcles. Rarely arise in the floor of 3rd ventricle (pars tuberalis extends up tuber cinereum, less calcification or cyst, uniform enhancement), sphenoid, nasopharynx, CP angle or pineal regions. Enhancing solid components. High T2

  • Adamantinomatous type – Usually children, predominantly cystic with cholesterol crystals in fluid (‘crankcase/machine oil’). High T1 from methaemoglobin or protein (not cholesterol or triglicerides), lobulated, encases vessels. Frequent calcification.
  • Papillary (squamous-papillary) type – Usually adults, predominantly solid with some cysts, usually low T1, spherical. Rarely calcifies.

Rathke Cleft Cyst

From squamous epithelial remants of Rathke’s pouch (neuroectoderm ascends from oral cavity to anterior lobe pituitary pars intermedia). Common (13% on autopsy), usually asymptomatic. Lined by single layer cuboidal or columnar cells. Usually starts between the anterior and posterior pituitary, extruding¬†suprasellar as it grows. 70% intra-and supra-sella, 25% anterior sella, 5% suprasellar. Most mucoid filled cyst, less common serous or desquamated debris in the cyst, hence variable T1, usually high T2. May have low T2 or nonenhancing nodule (dot sign, diagnostic), with low T2 occasionally completely filling the cyst. Rarely shows peripheral enhancing displaced pituitary tissue (cyst itself does not enhance). May compress structures causing hypopituitarism, diabetes insipidus, HA, visual field deficits; but usually asymptomatic. No calcification (cf craniopharyngioma) or soft-tissue mass. DDx craniopharyngioma, haemorrhagic pituitary.

Hamartoma of the Tuber Cinereum

Rare, M>F, precocious perberty, gelastic seizures, developmental delay, hyperactivity. Normal neuronal tissue in region of tuber cinereum (base of infundibulum) just anterior to the mamillary bodies. Iso T1 and high T2 to grey matter. Well-circumscribed, oval/round, stalk connects the mass to the tuber cinerum or mamillary bodies. Doesn’t tend to calcify, haemorrhage or enhance (cf craniopharyngioma and hypothalamic glioma).

Germinoma

Children and young adults. Diabetes insipidus, hypopituitarism, optic chiasm compression. From germ cells in suprasellar region. Hyperdense, uniform enhancement, may coexist with pineal mass. Doesn’t calcify. May metastasize with CSF seeding. Very sensitive to radiotherapy.

Pituitary Stalk Anomalies

Infundibulum shouldn’t be larger than the basilar artery. Enlargement in:

  • Granulomatous diseases – LCH, sarcoidosis, TB, Erdheim-Chester disease, lymphocytic hypophysitis.
  • Tumours – Pituitary adenoma, Rathke cyst, craniopharyngioma, germinoma, lymphoma, metastases, astrocytoma, stalk transection.

Other Suprasellar Lesions

  • Chiasmatic and hypothalamic glioma/astrocytoma.
  • Arachnoid cyst – 15% arise in suprasellar space ?lack of perforation of the membrane of Liliequist (between chiasmatic and interpeduncular cisterns).
  • Lipoma – Circumscribed, fat density.
  • Dermoid – Rarely arise in suprasellar region. Thick capsule with peripheral calcification.
  • Teratoma – May be large, contain dense calcification/ossification.
  • Epidermoid – Intradural or extradural. May be low T1, high T2, irregular with interstises (seen with intrathecal contrast), distorts local anatomy, may spread down clivus causing increased ‘space’ anterior to brainstem. Rarely enhance, occasionally rim calcification. Bright on FLAIR and DWI.
  • Meningioma – From tuberculum sellae, anterior clinoids, diaphragma sella, planum sphenoidale or upper clivus. Commonly narrow the ICA.