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The neurosurgeon performing hypophysectomies must master a learning curve and must be familiar with the most frequent complications of the operation to recognize them as early as possible and to treat them immediately and effectively. Urinary C/C ratios are sensitive indicators for the assessment of remission and recurrence of hyperadrenocorticism.

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Results-CT imaging enabled accurate preoperative localization of the pituitary. Appropriate positioning and surgical technique facilitated exposure of the pituitary and its extraction without hemorrhage. Postoperative recovery was generally uncomplicated. None of the eight dogs had somatotropic, gonadotropic, lactotropic, melanotropic, or posterior pituitary responses to stimulation at 10 weeks after hypophysectomy. Four dogs (ACTH nonresponders) also had no corticotropic response and four (ACTH responders) had small but significant responses in the combined anterior pituitary function test. Adrenocortical atrophy was more pronounced in the ACTH nonresponders than in the responders. No residual pituitary tissue was found along the ventral hypothalamic diencephalon but nests of pituitary cells were found embedded in fibrous tissue in the sella turcica. Conclusions-The surgical technique proved to be safe and effective. Microscopic nests of pituitary cells in the sella turcica may be responsible for residual corticotropic response to hypophysiotropic stimulation after hypophysectomy.Clinical Relevance-The surgical technique may be used in the treatment of dogs with pituitary-dependent hyperadrenocorticism. The corticotropic response is the most sensitive criterion in assessing completeness of hypophysectomy in dogs. OCopyright 1997 by The American College of Veterinaly SurgeonsHE SURGICAL technique of hypophysectomy T in dogs was first described at the beginning of this century, when dogs were used in experimental studies to examine the physiological role of the hypophysis.'" Because there was a high rate of mortality associated with the intracranial transtemporal approach, the transsphenoidal approach for ablation of the pituitary became the preferred technique in experimental studies in dog^.^-'^ From the late 1960s onwards, reports in the veterinary literature mentioned the use of hypophysectomy to treat pituitarydependent hyperadrenocorticism (PDH).'5-23 However, little clinical data were published and, despite its long history, hypophysectomy remained a rare procedure in clinical veterinary medicine. 15-17~19 This was mainly because of the high rate of complications associated with the procedure and the availability of alternative treatments for PDH (ie, bilateral adrena-From the