Abdominal Unicentric Castleman Disease: A Hepato-Pancreatico-Biliary Frenemy.

Castleman disease (CD) is a group of rare lymphoproliferative disorders characterized by shared histopathological features but distinct clinical entities, broadly classified into unicentric Castleman disease (UCD) and multicentric Castleman disease (MCD). UCD involves a single anatomical site and typically follows a benign clinical course, whereas MCD affects multiple lymph node stations and is associated with systemic symptoms and a more complex therapeutic approach. The disease is poorly understood, and the difficulty in reaching a diagnosis is well noted in the literature. While MCD is systemic and requires hematological work-up, abdominal UCD consists of a radiologically detected solitary mass that poses a diagnostic challenge, often necessitating a hepato-pancreatico-biliary (HPB) opinion. We report a retrospective case series of four patients diagnosed with UCD between 2011 and 2022 at a tertiary centre. All patients underwent extensive diagnostic work-up due to suspected malignancy based on radiological features and metabolic imaging. Surgical resection was performed in all cases, given diagnostic ambiguity or concern for malignancy. The cohort included three males and one female, aged 24 to 69 years. Lesions were located in the retroperitoneum, pancreaticoduodenal groove, small bowel mesentery, and adjacent to the caudate lobe. In one patient, UCD coexisted with a head of pancreas adenocarcinoma. In all cases, definitive diagnosis was established following surgical resection and histopathological analysis. One patient was found to have a coexisting focus of follicular dendritic cell sarcoma and remains free of recurrence 12 years post-resection. This rare association has been reported in the context of hyaline-vascular UCD and carries potential malignant behaviour, underscoring the need for long-term surveillance. All patients were referred to hematology services. UCD carries a low malignant potential; however, affected individuals may have an increased risk of developing lymphoproliferative disorders. HPB surgeons should maintain a high index of suspicion for this rare entity when evaluating retroperitoneal, paraduodenal, or mesenteric masses. In the majority of cases, surgical resection represents the culmination of an often complex diagnostic process that poses significant challenges to clinicians and leads patients to undergo surgery in the absence of a definitive preoperative diagnosis. Although complete surgical resection is considered curative and is typically associated with favourable outcomes, the future role of surgery may be subject to re-evaluation, particularly as advancements in radiological modalities could potentially facilitate non-invasive diagnosis. Regardless of the surgical outcome, all patients should be referred to hematology services for long-term follow-up. This case series underscores the diagnostic difficulties posed by UCD and highlights the importance of multidisciplinary collaboration in the management of such cases.