Incidence:  This is an extremely common tumor of rats, especially in Sprague-Dawley and Wistars.   Incidence varies with strain.  Tumors are more common in female than male rats.

Clinical Signs:  Pituitary adenomas may occasionally cause hydrocephalus resulting in depression or head tilt.  The tumors commonly secrete prolactin and secretion of milk may be observed in non-pregnant females.

Pathology:  Grossly, tumors are soft with an irregular surface and may have prominent hemorrhagic areas (A.).  They are generally well circumscribed and compress adjacent brain tissue (B.).  Closer magnification of the tumor cells can be seen in (C.).

Diagnosis:  Diagnosis can be made upon necropsy and histopathologic examination of tissue.