General
- Pituicytoma is a low-grade, non-functional neuroepithelial neoplasm of the sellar region.
- It is thought to arise from pituicytes, which are the primary glial cells of the posterior pituitary gland and infundibulum.
- Use to be grouped with the following but now known as a separate entity
- Granular cell tumour of the pituitary (a.k.a. pituitary choristoma)
- Pilocytic astrocytoma of the neurohypophysis
- ‘‘Posterior pituitary astrocytoma” and “infundibuloma”.
Definition
- Essential criteria
- Neoplasm composed of bipolar spindle cells arranged in sheets or short fascicles.
- Located in the sellar or suprasellar region.
- Nuclear expression of thyroid transcription factor 1 (TTF1).
- Absence of pituitary hormones and lineage-specific transcription factor expression.
- Absence of neuronal and neuroendocrine marker expression.
- Desirable criteria
- Absence of an interspersed reticulin fibre network.
Numbers
- Rare
- Since 2000 to 2016 only 70 cases World wide
- Adult 50 years (range: 7-83 years)
- M:F ratio is 1.5:1
- There is a slight reported male predominance.
Grading
- CNS WHO grade 1 tumour.
Histopathology
Macroscopic
- Solid
- Circumscribed
- Rarely has a cystic component
- Vary: firm, rubbery texture to consistency similar to normal brain
- Firmly adherent to adjacent structures in the suprasellar space.
- They are typically grey to yellow in colour.
Microscopic
- They are characterized by elongate, bipolar spindle cells arranged in solid sheets or short fascicles, occasionally exhibiting a storiform pattern.
- Neoplastic cells tend to have distinct cell borders and eosinophilic cytoplasm.
- Has rich blood supply
- They lack features such as eosinophilic granular bodies, Rosenthal fibres, or prominent cytoplasmic vacuolization.
- Infiltrative pattern is not present even though tumours can show adherence to adjacent structures in the suprasellar space
- While mitotic activity is typically low (Ki-67 index often < 3%), rare atypical cases with higher proliferation rates have been documented.
Immunophenotype
- +
- Consistent
- Vimentin
- S100 protein
- Nuclear staining for TTF1
- Inconsistent
- GFAP staining
- BCL2 staining
- EMA may show a patchy pattern that is cytoplasmic rather than membranous
- -
- Cytokeratin
- Pituitary hormones
- Neuronal or neuroendocrine markers (synaptophysin and chromogranin)
- NFP immunoreactivity is limited to axons in peritumoural neurohypophyseal tissue and is not present within the tumour
- Variable
- Strong reactivity is typical for S100 and vimentin, while GFAP expression is variable.
Pathogenesis
- Evidence suggests activation of the MAPK/ERK signalling pathway.
- Genetic alterations identified in some cases include somatic mutations in HRAS, NF1, and TSC1.
Localisation
- Arise along the distribution of the neurohypophysis, including the infundibulum / pituitary stalk and posterior pituitary.
- May be located in the
- Intrasellar
- Least common
- Suprasellar or
- In both the intrasellar and suprasellar compartments.
- Most present as suprasellar or sellar/suprasellar masses.
Cell of origin
- All share same nosological entity because all have nuclear expression of TTF1, suggesting that these three tumours may constitute a spectrum of a single nosological entity
- Pituicytomas
- Spindle cell oncocytomas,
- Granular cell tumours show
- Granular cell tumours occasionally occur in the CNS outside the pituitary gland (e.g. in the meninges, cerebral hemispheres, third ventricle, or cranial nerves); these tumours may be derived from glial cells, Schwann cells, or macrophages
- Pituicyte derivation
- Pituicyte: any of the glial cells of the posterior pituitary
- Ultrastructural studies have identified 5 distinct variants of pituicytes in the normal neurohypophysis:
- Light
- Most common
- Dark
- Small and electron-dense cytoplasm are called "dark"
- Ependymal
- Occasional cilia and/or microvilli projection
- Granular
- Light pituicytes numerous electron-dense lysosomal bodies, or phago-lysosomes.
- Granular cell tumours
- Oncocytic
- Light pituicytes with numerous mitochondria,
- Spindle cell oncocytomas
Clinical features
- Presentation is usually due to mass effect and is indistinguishable from other sellar lesions, including headaches, visual field defects, and hypopituitarism.
- Compression of the
- Optic chiasm
- Visual disturbance
- Infundibulum, and/or
- Pituitary gland.
- Features of hypopituitarism
- Fatigue, amenorrhoea, decreased libido, and mildly elevated serum prolactin (the stalk effect)
- Diabetes insipidus is reported to be uncommon.
- Slowly expansive nonhormonally active
- They have occasionally been found in association with synchronous functional pituitary adenomas.
Radiological features
General
- Generally indistinguishable from non-functioning pituitary adenomas on imaging.
CT
- Homogeneously enhancing at
- Pituitary fossa
- Suprasellar region.
- Size is variable, ranging from a few millimetres to a few centimetres.
MRI
- T1:
- Isointense solid mass;
- Posterior pituitary bright spot often absent
- Post pituitary bright spot due to stored vasopressin complex. This is highly proteinaceous that will slow down brownian motion to meet the lamour Fq, this will allow faster energy loss and hence shorter T1
- T1+C (Gd): bright contrast enhancement
- T2: heterogeneous, hypointense to isointense
DSA
- Pituicytomas have a rich capillary network, accounting for their usual contrast enhancement and propensity to bleed at surgery. They receive their blood supply from the normal and extensive supply
Management
- The primary management for pituicytoma is gross total surgical excision.
- Local adherence of pituicytomas to regional structures may preclude complete resection
- Residual disease may gradually regrow over a period of several years
Prognosis
- These are typically benign, slow-growing neoplasms.
- They are generally curable by complete surgical removal and have a low rate of recurrence compared to spindle cell oncocytoma.
- No correlation of proliferation with clinical outcome
- No instances of malignant transformation or distant metastasis have been reported to date.
Differential diagnosis
- Importantly for the differential diagnosis with pilocytic astrocytoma and normal neurohypophysis, pituicytomas show no Rosenthal fibres, eosinophilic granular bodies, or Herring bodies (axonal dilatations for neuropeptide storage in the neurohypophysis)
- Unlike schwannomas, reticulin staining shows no pericellular pattern.
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