Pituitary lymphoma

Pituitary lymphoma is very rare, although lymphomatous (or leukaemic) infiltration of the perisellar dura is not infrequently encountered as part of more widespread CNS disease. This article concerns itself with involvement of the pituitary itself rather than the region more broadly. For a general discussion please refer to primary CNS lymphoma.

As is the case with CNS lymphoma elsewhere, pituitary lymphomas can either be primary (no systemic disease) or secondary (involvement of the pituitary gland is part of systemic disease). 

Epidemiology

Pituitary lymphoma (i.e. parenchymal disease limited to the pituitary gland rather than dural involvement, or extension of cerebral primary CNS lymphoma to the region) is very rare, accounting for 0.1 - 0-0.3% of pituitary tumours ¹. Ture primary lymphoma of the CNS is even less common, with only a smattering of cases reported ^1-3. 

Clinical presentation

Pituitary function is usually not impaired, and lymphoma of the pitutiary is usually identified either incidentally or as the result of increased uptake when imaging the whole body.  Occasionally patients present as a result of the syndrome of inappropriate antidiuretic hormone (SIADH) ². Rarely the tumour is large enough to cause mass effect upon the optic chiasm ².  

Pathology

As is the case with primary CNS lymphoma, the majority of primary pituitary lymphomas are non-Hodgkin B-cell lymphomas ^1-3. 

Radiographic features

As is the case with other pituitary region masses, MRI is the modality of choice for evaluation of suspected pituitary lymphoma.

MRI

Lymphomatous masses share similar signal intensity irrespective of their location, influenced by the tightly packed cellularity of these tumour and high nucleus-to-cytoplasm ratio of lymphoma ³. They appear as solid masses. 

• T1: iso- to hypointense
• T2: iso-to hypointense
• T1 C+:
  • vivid contrast enhancement
  • may be heterogeneous even in immunocompetent hosts (unlike cerebral lymphoma)

Differential diagnosis

The differential is primarily that of solid and enhancing  pituitary region masses, with the main differentials being:

• pituitary adenoma:
  • may appear indistinguishable 
  • usually higher signal on T2
  • more evidence of slow growth
• craniopharyngioma (papillary):
  • often has a cystic component (albeit a minor one)
• pituitary metastases:
  • may appear indistinguishable
  • usually higher signal on T2 
• lymphocytic hypophysitis:
  • may appear indistinguishable
  • usually different demographic (young women most commonly affected)