NRAS-mutated oncocytic benign liver lesion in an organ donor: Pitfalls and troubles in frozen section diagnosis and risk assessment.

BACKGROUND: In the transplant setting, the definition of the risk of neoplastic transmission from donor to recipient often requires intraoperative pathological evaluation on frozen sections. Although most lesions can be easily classified into acceptable or unacceptable risk according to the Italian National Guidelines, there are cases in which unusual histologic features cannot be further investigated because of the lack of ancillary techniques on frozen sections. CASE PRESENTATION: Here we present a case of a liver lesion in a 51-year-old male donor, subjected to histopathological on-call examination. The frozen sections showed a well-demarcated lesion consisting of epithelioid cells disposed in laminar structures and intermingled with a dense lymphocytic population: this led to organ discard with interruption of the donation process. The definitive histological analysis required an extensive immunohistochemical (IHC) investigation: the final diagnosis was "bile duct adenoma with oncocytic features", eventually confirmed by a strongly positive anti-mitochondrial IHC. Finally, an NGS panel analysis was performed, which revealed NRAS mutation. DISCUSSION: To the best of our knowledge, this is the first case of oncocytic bile duct adenoma confirmed by anti-mitochondrial IHC and with NRAS mutation. The most challenging aspect of this case was represented by the transplant setting. In fact, the oncocytic features and the dense lymphocytic infiltrate represented concomitant unusual histological features that led to the halt of the organ donation procedures.

Multifocal Fibrosing Thyroiditis: an Under-recognized Mimicker of Papillary Thyroid Carcinoma.

Multifocal fibrosing thyroiditis (MFT) is an enigmatic entity, characterized by multiple fibrotic scar-like lesions with a paucicellular fibrotic center surrounded by a cellular peripheral area with reactive-appearing follicular cell atypia and variable chronic inflammation. Although poorly recognized and likely underreported in surgical pathology, the entity is considered rare with only 65 cases to date-including the current one reported to expand on the preoperative findings of this under-recognized entity. The average age of the patients is 46.8 years (range 15-71 years), 94% are female, with female to male ratio of 15:1. Individual MFT lesions typically have a superficial location. The average number of fibrotic lesions is 15.4 (range 2-51 per MFT case). Their average size is 3.1 mm (range 0.4-15.1). MFT is a disorder of diseased thyroids, typically found postoperatively in glands removed for other reasons, such as chronic lymphocytic/Hashimoto thyroiditis (32.3%), follicular nodular disease (nodular hyperplasia) (30.1%), hyperthyroidism/diffuse hyperplasia (Graves disease) (9.2%). Intriguing is the association with papillary thyroid carcinoma-present in 38.5% of MFT cases, and particularly with sub-centimetric and multifocal papillary thyroid carcinoma, with which MFT can be confused. Cases where MFT is the only thyroid pathology (7.7%) can be preoperatively mistaken for papillary thyroid carcinoma, due to worrisome ultrasound (US) and cytologic features, both of which are here documented for the first time as a component of this article. Wider recognition of MFT and of its cytologic and ultrasound features at preoperative evaluation may reduce unnecessary thyroidectomies.