Pituitary abscess

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Pituitary abscesses are rare and represent infection of the pituitary gland by organisms, most commonly bacteria.

Epidemiology

Pituitary abscesses represent less than 1% of all pituitary masses and so seem to have gender predilection . Although many cases do not appear to have a predisposing factor, in some patients immunosuppression, prior surgery or infection elsewhere in the body are identified .

Clinical presentation

Often, the presentation is relatively indolent without overt features of infection . Symptoms include those from mass effect (e.g. bitemporal hemianopia and headaches), endocrinological dysfunction (e.g. loss of libido, polydipsia, polyuria, amenorrhea) and only sometimes (~25%) infective symptoms (e.g. fevers and meningism) .  As such pituitary abscesses are often not diagnosed pre-operatively but rather are thought to be the far more common pituitary adenoma that not infrequently demonstrate cystic/necrotic degenerative change.

Pathology

As is the case with many other infections, the route of infection is varied and can be haematogenous, extension from an adjacent infection (e.g. sphenoid sinusitis) or direct inoculation after surgery .

In the majority of cases (70%) the underlying pituitary is normal prior to infection . These are sometimes referred to a 'primary' pituitary abscess. In contrast, 'secondary' pituitary abscesses are those that arise in a previously abnormal pituitary (e.g. existing tumor) .

Microbiology

A wide variety of pathogens have been isolated from pituitary abscesses, including :

  • bacteria
    • Staphylococcus spp and Streptococcus spp (most common)
    • Neisseria spp, Citrobacter spp, E. coli, Brucella, Salmonella etc... 
  • mycobacterium
  • fungus (most common in immunosuppressed patients)
    • Aspergillus, Candida and Histoplasma

Radiographic features

CT

CT of the brain and base of the skull may demonstrate a low central attenuating mass. With the administration of contrast, vivid peripheral contrast enhancement is usually present.

Thin bone reformats usually do not demonstrate significant enlargement of the sella as the lesion has only been present for a relatively short time, however, erosion of bone may be seen as may evidence of adjacent infection.

MRI

MRI is the modality of choice for evaluating a patient suspected of having a pituitary abscess. It will demonstrate features of an abscess; peripherally enhancing mass with central high T2 signal, high DWI signal and low ADC values. It should be noted, however, that macroadenomas with hemorrhagic change may have similar appearances.

Treatment and prognosis

Treatment is surgical with transsphenoidal hypophysectomy, drainage, and antibiotics . Pituitary function often does not recover and long-term hormone replacement is necessary .

Differential diagnosis

The main differential is that of other pituitary masses, particularly: