Reticulin Framework Assessment in Neoplastic Endocrine Pathology

The reticulin framework, composed mainly of type III collagen, is an essential structural component of biological tissues. Reticulin stains, particularly silver-based methods, enable detailed visualization of reticulin framework alterations, which have been proven to be quick, low-cost, and reliable solutions for highlighting quantitative and qualitative changes of reticulin framework and have been variably associated with neoplastic and non-neoplastic conditions. This review provides an updated overview of reticulin stain applications and reticulin framework assessment in endocrine and neuroendocrine neoplasms, including those of the pituitary, parathyroid, adrenal, and other neuroendocrine systems. In pituitary neuroendocrine tumors, reticulin framework loss serves as a distinguishing feature between normal and neoplastic adenohypophysis. Parathyroid neoplasms, including adenomas, atypical tumors, and carcinomas, exhibit varying degrees of reticulin framework disruption, which may aid in differential diagnosis. Similarly, in adrenocortical neoplasms, reticulin framework evaluation plays a crucial role in malignancy assessment, as defined in the reticulin algorithm, which incorporates reticulin framework alterations alongside three Weiss criteria: necrosis, high mitotic count (> 5/10 mm²), and venous invasion. Moreover, specific reticulin framework patterns help to distinguish the different morphological subtypes of bilateral macronodular adrenocortical disease. Pheochromocytomas and paragangliomas display a range of reticulin framework patterns which might be related to the genetic background of the tumor. Finally, different neuroendocrine neoplasms exhibit variable reticulin framework integrity, with a more significant disruption observed in high-grade carcinomas. Advancements in digital pathology and artificial intelligence offer promising avenues for automated reticulin framework quantification, enhancing diagnostic precision and prognostic assessments. The integration of computational approaches may further improve the clinical utility of reticulin framework evaluation in endocrine pathology.