Study of long-term survival after transsphenoidal hypophysectomy in clinically normal dogs.

Experimental hypophysectomies were performed in 7 clinically normal dogs, using a new modification of the transsphenoidal approach. This approach facilitated centering of the sphenoid bone trephination and allowed safe exposure of the hypophysis regardless of the size or shape of a dog's skull. Complications did not occur during surgery and all dogs recovered well from surgery. Growth hormone secretory capacity was measured over a 3-month period to assess completeness of hypophysectomies. One dog was euthanatized 2 months after surgery, 4 dogs were euthanatized at 3 months after surgery, and 2 dogs were allowed to survive and their progress was followed for 2.5 years. Soft palate dehiscence and keratoconjunctivitis sicca developed in 2 of the dogs. The technical deficiencies responsible for these complications were corrected shortly after the beginning of the study. In 4 of the 5 necropsied dogs, minute remnants of adenohypophyseal tissue were found in the sellae turcica. Measurement of in vivo growth hormone secretory capacity revealed that these remnants had an altered stage of functional activity. Although complete hypophysectomy was not achieved consistently, the main technical obstacle of hypophysectomy, the reliable identification and the avoidance of the vascular structures surrounding the hypophysis, has seemingly been overcome. The surgical technique proved to enhance the safety of hypophysectomy, and the procedure can be recommended to treat clinical cases of canine pituitary-dependent hyperadrenocorticism. The clinical significance of potential subtotal hypophysectomy remains yet to be evaluated.