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High-risk pituitary adenomas are aggressive. They show clinical and imaging features similar to those of carcinomas, including infiltration of the surrounding brain structures, but lack cerebrospinal or systemic metastases. In addition, they display distinct behavior, including tendency for fast growth and frequent recurrences, which are difficult to control. The term “high-risk” adenoma was first introduced in the 4th edition of the World Health Organization Classification of Endocrine Tumors in 2017. Five defined adenoma types belong to this category, including sparsely granulated somatotroph, lactotroph in men, Crooke cell, silent corticotroph, and plurihormonal PIT-1 positive adenomas. The morphological and immunohistochemical characteristics of high-risk adenomas are herein described in detail. In addition, the clinical features and the treatment options are presented. This review focuses on predictive markers assessed by immunohistochemistry, which help clinicians to design the appropriate treatment strategies for high-risk adenomas. Somatostatin receptor status predicts effectiveness of postsurgical treatment with somatostatin analogs, and MGMT expression predicts response to treatment with temozolomide. This comprehensive review presents the clinical and pathological features of high-risk pituitary adenomas, underlines the contribution of immunohistochemistry, and emphasizes the leading role of pathology in the design of optimal clinical management.

Double and multiple adenomas of the pituitary are composed of two or more distinct tumors located in the same gland. They represent uncommon lesions measuring less than 1 cm, reported as having a low incidence in autopsies and occurring even more infrequently in surgical series. The histological diagnosis of double adenomas in surgical material is often extremely difficult, and confirmation requires immunohistochemistry and, occasionally, electron microscopy. Fragmented tissue material submitted for histology after transsphenoidal resection complicates the diagnosis. Difficulties in demonstrating double or multiple adenomas by imaging techniques contribute to diagnostic failure. Magnetic resonance imaging (MRI) techniques may disclose two separate adenomas located in the same pituitary gland. Intraoperative MRI and imaging ultrasonography, together with positron emission computed tomography, more accurately identify sites of residual tumors. These techniques might also detect postoperatively a residual tumor belonging to the second component of double adenoma. Double adenomas may also create extreme clinical diagnostic challenges. It is almost impossible to suspect functioning double adenomas with combined hormone secretion, each one secreting a different hormone, and distinguish them from an isolated plurihormonal adenoma, simultaneously secreting more than one hormone. Double adenomas may underlie surgical failure when one adenoma is removed while the other is left behind. Despite the low frequency of double adenomas, identification and resection of both of them is of major importance for the achievement of biochemical cure.

OBJECTIVE: The term “null cell”adenoma was first proposed in 1980 to designate pituitary adenomas lacking clinical, biochemical and morphological markers to disclose their cell origin. DESIGN: The aim of this study was to investigate the presence of α- and β-gonadotropin subunits in clinically nonfunctioning pituitary tumors, which were initially immunonegative and thus diagnosed as null cell adenomas. For this reason, we reapplied immunohistochemistry using a more sensitive method comprising a tyramide signal amplification technique, combined with a polymer antibody immunohistochemical detection system. RESULTS: With this approach, all these previously negative tumors became positive for α- and α-gonadotropin hormone subunits. CONCLUSIONS: Our results prove that so-called “null cell”adenomas produce α-SU or/and β-FSH or β-LH and therefore are gonadotrph adenomas in origin.

The purpose of this study was to detect in vitrogrowth hormone (GH) and prolactin (PRL) secretion from adenomas clinically associated with GH or PRL hypersecretion. The reverse hemolytic plaque assay (RHPA) was applied in order to reveal possible differences among various morphologic adenoma types, and to examine the inhibitory effects of octreotide on GH release as well. The 20 surgically resected pituitary adenomas studied included 15 from acromegalic patients and 5 from patients with hyperprolactinemia. All adenomas were diagnosed by histology, immunocytochemistry and electron microscopy. Among tumors associated with acromegaly, 5 were densely granulated (DG), 5 were sparsely granulated (SG) somatotroph (SM) adenomas, 2 were mammosomatotroph (MSM) and 3 mixed somatotroph-lactotroph cell (mixed SM-LT) adenomas; tumors causing hyperprolactinemia included 4 lactotroph (LT) adenomas and 1 mixed SM-LT adenoma. GH release assessed by the RHPA corresponded to in vivohormone secretion and to tissue immunoreactivity. Statistical analysis showed significant differences among all morphologic types of SM adenomas, exclusive of SG-SM adenomas compared to mixed SM-LT adenomas. The mean plaque size in DG-SM and MSM adenomas was significantly greater than that of SG-SM and mixed SM-LT adenomas, indicating higher GH secretion by the former two types during the same incubation time. PRL secretion was documented in 2 mixed SM-LT adenomas. Plaques for PRL, but not for GH were formed in all LT adenomas. In all SM and LT adenomas, cells producing large plaques represented a minority of the plaque-forming cell population, however, they accounted for the largest part of the total plaque area, thus the largest part of hormone secretion. Octreotide effects on GH release were studied in 6 adenomas by the RHPA. Octreotide treatment induced a rapid and significant reduction in GH secretion by SM cells in vitro, with a selective effect on high-secreting cells.