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Pituitary metastasis

Pituitary metastases are rare, and unless systemic metastatic disease is already apparent, are often preoperatively misdiagnosed as pituitary adenomas. 

Epidemiology

The demographic of affected patients reflects that of underlying primary tumours, which are most frequently breast cancer in women and lung cancer in men; thus elderly patients are most commonly affected 1-2. Pituitary metastases account for a minority of all intracranial metastases, although the figures vary widely from publication to publication 1.  

Clinical presentation

Clinical presentation is variable but includes 1

  • hormonal disfunction
    • diabetes insipidus
      • common: 29 - 71% 3
      • presumably due to predilection for posterior pituitary involvement (see below)
    • pan hypopituitarism
    • hyperprolactinaemia: disruption of the normal inhibition of prolactin release by dopamine
  • mass effect
    • optic chiasm compression
    • extension into carvernous sinuses

Pathology

The most common primary malignancies to be found in the pituitary are breast cancer in women and lung cancer in men, presumably merely due to the large number of cerebral metastases from these two cancers 2. Many other primary tumours have also been described 3

It is interesting to note that the posterior lobe and the infundibulum of the pituitary gland are more frequently involved than the anterior lobe (although this may not be the case in breast cancer 3), presumably due to the fact that the anterior pituitary receives its blood via the portal circulation rather than directly form the hypophyseal arteries 1

Radiographic features

Although larger lesions are visible on CT, appearing as enhancing soft tissue masses, MRI is the modality of choice for assessment of the pituitary region. 

MRI

Although all metastases to the pituitary (as is the case everywhere) start as microscopic deposits, they are usually encountered in two patterns:

  1. sizeable mass arising from the pituitary fossa (similar to a macroadenoma)
  2. infundibular lesion

Small intrasellar masses are usually not identified, mainly because they are presumably asymptomatic and require targeted sequences which are not performed without indication. 

Sizeable mass

These masses typically involve both the intra and suprasellar compartments. As they are usually rapidly growing they have a number of features which are helpful in distinguishing them from pituitary macroadenomas 

  • relatively normal size fossa
  • bony destruction rather than remodelling
  • dural thickening
  • dumb-bell shape as the diaphragma sella has not had time to be stretched
  • irregular edges
Infundibular lesion

Involvement of the infundibulum typically appears as nodular / irregular thickening and enhancement. The posterior pituitary bright spot may also be absent, either from interruption of the normal transport of neurosecretory granules down the infundibulum, or due to concurrent infiltration of the posterior lobe.

Treatment and prognosis

Treatment is usually reserved for patients with symptomatic lesions (e.g. visual failure due to chiasmatic compression) or those in whom the diagnosis is not obvious (e.g. not known to have a malignancy, or thought to be in remission). Surgical decompression and biopsy in both cases can be carried out, although the overall prognosis and physical reserves of the patient need to be taken into account. 

Whole brain radiotherapy is  also an option when the pituitary lesion is one of many cerebral metastases 3. The proximity to the optic chiasm usually makes radiosurgery impractical without leading to loss of vision 3

Prognosis is difficult to estimate as it will vary significantly depending on the disease of systemic disease and the primary histology, although as a general ballpark figure a mean survival of approximately 6 months is in line with the published literature 3

DIfferential diagnosis

The differential diagnosis for pituitary metastases is broadly that of pituitary region masses, and generally can be narrowed depending on the morphology of the lesion. 

Solid and enhancing pituitary region masses has a differential which includes: 

Nodular thickening and enhancement of the infundibulum has a differential which includes 1

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