Chromophobe adenoma; pituitary adenoma;
undifferentiated cell adenoma; an adenoma of the hypophysis composed
of cells for which there is no overt evidence or hormone production,
but which produce hypopituitarism and visual disturbances by
compression of adjacent structures; approximately one third of these
tumors have cells with abundant mitochondria (oncocytes) that are
somewhat larger than the monocytic null cells.
On plain films the pituitary will appear enlarged.
MRI is now the technique of choice for imaging the sella and
juxtasellar regions. Compared to CT, MRI has much improved soft
tissue resolution and avoids bony artefacts and ionising radiation.
The multiplanar capability of MR allows direct imaging in all three
planes. Current imaging protocols for the hypothalamic-pituitary
axis typically utilise sagittal and coronal T1-weighted spin-echo
sequences. In order to achieve high spatial resolution thin slices
(3 mm) and a small field-of-view (16-20 cm) are used.
Pituitary CT can be performed in the axial plane with thin (1.0 mm)
contiguous sections following 100mls intravenous contrast medium.
Exposure parameters approximate to around 120kV, 200 mA and 2 second
scan time and a soft tissue algorithm is used. Images can usefully
be reformatted in the coronal and sagittal planes. Alternatively,
thin sections in the coronal plane with the patient prone and the
neck extended allow pituitary abnormalities to be demonstrated with
a lower radiation dose to the lens than is possible with axial
Chromophobe adenomas will present clinically as either
a space-occupying lesion or a trophic hormone insufficiency, 25% of
these lesions secrete (usually prolactin). Hormonal deficits develop
slowly, so these tumors may be greatly enlarged prior to clinically
accessible hormone deficiencies. Cells comprising there tumors are
composed of sparsely granulated cytoplasm, as seen in this slide.
Immunohistiochemical techniques fail to demonstrate any hormonal
function in these cells. A varient chromophobe adenoma has small,
undifferentiated cells with only a scant, cleared cytoplasm, and are
called "null cell adenomas". 25% of all pituitary tumors removed
surgically are nonfunctional pituitary adenomas.
The development of transsphenoidal hypophysectomy represents a major
development in the safe surgical treatment of both hormonally-active
and nonfunctioning tumors. Transsphenoidal surgery is the usual
treatment of choice for lesions confined within the sella turcica.
Lesions extending beyond the confines of the pituitary are most
frequently the nonfunctioning chromophobe adenomas and require
additional radiation therapy. Rapid deterioration of vision is an
immediate indication for surgery (to relieve pressure produced by
the growing tumor mass).