Objective: The microsurgical pseudocapsule can be found in the transition zone between an adenoma and the surrounding normal pituitary tissue. We investigated the precise histology of the pseudocapsule. Furthermore, we evaluated the remission rate, the changes in pituitary function, and the recurrence rate after intensive resection of the pseudocapsule.
Methods: In 616 patients with pituitary adenomas (Hardy Types I-III) over a period of 14 years, we introduced intensive resection of the microsurgical pseudocapsule to achieve complete tumor removal. A combined pituitary function test and radiological study were performed on the patients before surgery, 1 year after surgery, and at subsequent 1.5-year intervals 2 to 13 years postoperatively.
Results: Microsurgical pseudocapsules were identified in 343 (55.7%) of 616 patients, and the distinct microsurgical pseudocapsules were observed in 180 (52.5%) of these patients. In the remaining 163 patients, the microsurgical pseudocapsules were incompletely developed. Tumor cluster infiltration was present in the pseudocapsule in 71 (43.6%) of these patients. Aggressive resection of the microsurgical pseudocapsule was more often required in larger tumors than in smaller ones. The presence of a pseudocapsule was slightly more frequent in prolactin-secreting tumors (70.9%) than in growth hormone-secreting (55.0%) and adrenocorticotropic hormone-secreting (40.0%) tumors. In the 243 patients of the total resection group who underwent combined pituitary function tests more than 2 times after surgery, the surgical remission rate was 99.1% in clinically nonfunctional tumors, 88% in growth hormone-secreting, 70.6% in prolactin-secreting, and 100% in adrenocorticotropic hormone-secreting tumors. The surgical remission rate was 86.2% in the presence of a pseudocapsule and 94.3% in the absence of a pseudocapsule. Preoperative hypopituitarism improved in 140 patients (57.6%), persisted in 47 patients (19.3%), and was aggravated in 33 patients (13.6%). There was no statistical difference in improvement or deterioration of pituitary function according to the existence or absence of the pseudocapsule. The tumor recurrence rate was 0.8% in the total resection group and was 42.1% in the subtotal resection group.
Conclusion: We have shown that tumor tissue is frequently present within the pseudocapsule, suggesting that any tumor remnant in the pseudocapsule could be a source of recurrence and an obstacle to achieving complete remission. These results indicate that intensive resection of the pseudocapsule could result in a higher remission rate without deteriorating pituitary function.