Pseudomyxoma Peritonei Secondary to Mucinous Adenocarcinoma of the Appendix: A Rare Case Report

Abstract

Background: Pseudomyxoma peritonei (PMP) is an uncommon condition characterized by the accumulation of mucinous material within the peritoneal cavity and is most commonly associated with appendiceal mucinous neoplasms. Although computed tomography (CT) and ¹⁸F-FDG PET/CT are commonly used for disease evaluation, ultrasonography may demonstrate characteristic morphological features that provide important diagnostic clues.
Case summary: A 57-year-old man with a history of mucinous adenocarcinoma of the appendix, previously treated with diagnostic
laparoscopy, appendectomy, and chemotherapy, underwent follow-up imaging. Ultrasonography demonstrated a large multiloculated intraperitoneal collection containing multiple thin internal septations and low-level internal echoes in the right upper abdomen and perihepatic region, producing characteristic scalloping of the right lateral hepatic surface. No definite peritoneal nodules or omental thickening were identified. Subsequent ¹⁸F-FDG PET/CT demonstrated a corresponding loculated collection along the right lateral, anterior, and posteroinferior aspects of the right hepatic lobe, with low FDG uptake (SUV_max 1.80) and associated hepatic scalloping. Ultrasound-guided aspiration yielded thick, gelatinous mucinous material. Cytopathological examination demonstrated abundant extracellular mucin containing mucin-producing neoplastic epithelial cells, confirming peritoneal involvement by mucinous neoplasm.
Conclusion: In patients with a history of appendiceal mucinous neoplasia, recognition of a multiloculated mucinous intraperitoneal
collection with characteristic visceral scalloping on ultrasonography can provide an important diagnostic clue to PMP, even in the absence of discrete peritoneal or omental deposits. Dynamic correlation with CT or ¹⁸F-FDG PET/CT and image-guided aspiration may further aid diagnosis and characterization.

BJusg. vol. 27, no. 1, June 2026, Page: 50-54