The presence of a histological pseudocapsule around pituitary tumors was noted in the early 1900s. Since that time there has been no emphasis on the sequence of the stages of its development or on the relationship between these stages and the capacity to identify very small pituitary tumors at surgery in patients in whom preoperative imaging has been nondiagnostic. In addition, limited emphasis has been given to the pseudocapsule’s use for selective and complete resection of pituitary adenomas.
The development of the pseudocapsule was examined by performing histological analysis of portions of pituitary glands removed during 805 operations for Cushing disease.
Twenty-five adenomas, each measuring between 0.25 and 4 mm in maximum diameter, were detected in the excised specimens; 17 were adenocorticotropic hormone–positive adenomas and eight were incidental tumors (four prolactin-secreting and four nonsecreting lesions). In 16 tumors the size of the adenoma could be established. The distribution of tumor size in relation to the presence of a histological pseudocapsule indicates a transition from the absence of a reticulin capsule (tumor diameter ≤ 1 mm) through the initial compression of surrounding tissue (tumor diameter 1–2 mm) to the presence of a multilayered reticulin capsule observed when adenomas become larger (tumor diameter 2–3 mm).
The absence of a reticulin capsule in cases of very small tumors may contribute to limited localization of these lesions during surgical exploration of the pituitary gland. In this article the authors describe surgical techniques in which the histological pseudocapsule is used as a surgical capsule during pituitary surgery. In their experience, recognition of this surgical capsule and its use at surgery has contributed to the identification of microadenomas buried in the pituitary gland, aided the recognition of subtle invasion of the pituitary capsule and contiguous dura mater, and enhanced the consistency of complete tumor excision with small and large tumors.
Abbreviations used in this paper: ACTH = adrenocorticotropic hormone; MR = magnetic resonance; PRL = prolactin.
DasKSpencerWNwagwuCISchaefferSWenkEWeissMH: Approaches to the sellar and parasellar region: anatomic comparison of endonasal-transsphenoidal, sublabial-transsphenoidal, and transethmoidal approaches. Neurol Res23:51–542001
FarnoudMRKujasMDeromePRacadotJPeillonFLiJY: Interactions between normal and tumoral tissues at the boundary of human anterior pituitary adenomas. An immunohistochemical study. Virchows Arch424:75–821994
OldfieldEHChrousosGPSchulteHMSchaafMMcKeeverPEKrudyAG: Preoperative lateralization of ACTH-secreting pituitary microadenomas by bilateral and simultaneous inferior petrosal venous sinus sampling. N Engl J Med312:100–1031985
SchulteHMOldfieldEHAllolioBKatzDABerkmanRAAliIU: Clonal composition of pituitary adenomas in patients with Cushing’s disease: determination by X-chromosome inactivation analysis. J Clin Endocrinol Metab73:1302–13081991
WatsonJCShawkerTHNiemanLKDeVroomHLDoppmanJLOldfieldEH: Localization of pituitary adenomas by using intraoperative ultrasound in patients with Cushing’s disease and no demonstrable pituitary tumor on magnetic resonance imaging. J Neurosurg89:927–9321998