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Pituicytoma

Dr Frank Gaillard et al.

Pituicytomas are rare tumours arising from pituicytes, a specialised glial cell in the neurohypophysis and infundibulum of the pituitary gland. There is much confusion in the literature as to what exactly a pituicytoma is, with the term used to synonymously particularly in older literature by some authors for a number of other tumours (now recognised to be separate lesions, including ^1,3-4:

granular cell tumour of the pituitary (aka pituitary choristoma)
pilocytic astrocytoma of the neurohypophysis (aka infundibuloma)

Epidemiology

Peak Incidence is in the 5^th decade, with no cases less than 20 years old. There is a recognised female predilection with M:F ratio of 1:2

Clinical presentation

Clinical presentation is either from endocrine dysfunction (amenorrhea, galactorrhea, infertility, diabetes insipidus, panhypopituitarism) or from compression of adjacent structures, typically the optic chiasm. Many are asymptomatic, with the lesion only found incidentally.

Pathology

Pituicytomas are considered WHO Grade 1 tumours and are usually indolent.

Macroscopically these tumours are well circumscribed, soft to medium consistency with a gray to yellow homogeneous or granular cut surface. Necrosis and cystic degeneration are uncommon.

Histologically they are fibrillary astrocytomas, with rich blood supply. The cells are spindle or stellate in shape and syncytial fibrillary cytoplasm ¹. They stain diffusely for S-100 and vimentin. GFAP and EMA are variably positive ¹. Ki-67 is usually less than 2% ¹.

Radiographic features

CT

Typically these masses a homogeneously enhancing, either with the pituitary fossa or in the suprasellar region. Size is variable, ranging from a few millimetres to a few centimetres.

MRI

T1 : iso intense solid mass, posterior pituitary bright spot often absent
T1 C+ (Gd) : bright contrast enhancement
T2 : heterogenous , hypo intense to iso intense

DSA

Pituicytomas have a rich capillary network, accounting for their usual contrast enhancement and propensity to bleed at surgery. They receive their blood supply form the normal and extensive supply to the pituitary gland, including the meningohypophyseal trunk and superior hypophyseal arteries.

Treatment and prognosis

As the tumours are benign and slow growing, if asymptomatic then expectant management is sufficient. If mass effect is present then resection may be required. Caution should be exercised as these tumours are highly vascular which my lead to difficulties with a routine transphenoidal approach.

Complete resection can be difficult due to the structures involved and local recurrence is common ¹.