Transsphenoidal hypophysectomy for treatment of pituitary-dependent hyperadrenocorticism in 7 cats

Objective-Evaluation of microsurgical transsphenoidal hypophysectomy for th e treatment of pituitary-dependent hyperadrenocorticism (PDH) in cats. Study Design-Prospective clinical study. Animals or Sample Population-Seven cats with PDH. Methods-Urinary cortisol/creatinine ratios, pituitary-adrenocortical functi on tests, and computed tomography (CT) were performed on 7 cats that presen ted with a provisional diagnosis of hyperadrenacorticism. All cats underwen t microsurgical transsphenoidal hypophysectomy with histologic examination of the excised specimen. Follow-up consisted of clinical evaluation, repeat adrenocortical function testing, and CT. Results-Four cats had concurrent diabetes mellitus. In all cats, the urinar y cortisol/creatinine (C/C) ratios were elevated. The dexamethasone screeni ng test showed that 2 cats did not meet the criterion for hyperadrenocortic ism. The response of the cats' plasma concentrations of cortisol and adreno corticotrophic hormone to a high dose of dexamethasone varied from very sen sitive to completely dexamethasone resistant. Basal plasma alpha -melanocyt e-stimulating hormone concentrations were elevated in 2 cats with a pars in termedia adenoma and in 3 cats with an adenoma that originated from the ant erior lobe. Preoperative CT enabled accurate assessment of pituitary size ( 5 nonenlarged pituitaries with a height <4 mm and 2 enlarged pituitaries wi th a height >5 mm) and localization relative to intraoperative anatomic lan dmarks. Two cats died within 4 weeks after surgery of a nonrelated disease. In the remaining 5 cats, the hyperadrenocorticism went into both clinical and biochemical remission. Hyperadrenocorticism recurred in 1 cat after 19 months, but no other therapy was given and the cat died at home 28 months a fter surgery. CT evaluation of this cat had identified pituitary remnants 6 weeks after surgery. The main postoperative complications were oronasal fi stula (1 cat), complete dehiscence of the soft palate (1 cat), and transien t reduction of tear production (I cat). One cat died at 6 months (undefined anemia), and another cat at 8 months (recurrent nose and middle ear infect ion secondary to soft palate dehiscence) after surgery. In the surviving 2 cats, the remission periods at the time of writing were 46 and 15 months. I n the 2 cats with sufficient follow-up time, the concurrent diabetes mellit us disappeared, ie, insulin treatment could be discontinued at 4 weeks and 5 months after hypophysectomy. In all 7 cats, the histologic diagnosis was pituitary adenoma. Conclusions-Microsurgical transsphenoidal hypophysectomy is an effective me thod of treatment for feline PDH in specialized veterinary institutions hav ing access to advanced pituitary imaging techniques. Concurrent diabetes me llitus is usually reversible after hypophysectomy. Thorough presurgical scr eening for coexisting diseases is imperative. Clinical Relevance-PDH in cats can be effectively treated by hypophysectomy . The neurosurgeon performing hypophysectomy must master a learning curve a nd must be familiar with the most frequent complications of the operation t o treat them immediately and effectively. Urinary C/C ratios are sensitive indicators for the assessment of remission and recurrence of hyperadrenocor ticism. (C) Copyright 2001 by The American College of Veterinary Surgeons.