Low-Grade Appendiceal Mucinous Neoplasm: A Case Series

Abstract

Low-grade appendiceal mucinous neoplasm (LAMN) is a lesion of the appendix with potentially fatal consequences if untreated. Though LAMN can be asymptomatic and stable, it can rupture and seed mucin and neoplastic epithelium into the peritoneum, leading to pseudomyxoma peritonei (PMP), a serious complication characterized by intraperitoneal accumulation of mucinous tumors and ascites with a high morbidity and mortality rate. Therefore, timely identification and treatment of LAMN are crucial for reducing PMP risk and improving prognosis and outcome. This case series sought to examine five LAMN cases and delineate the strategies for managing LAMN and progression to rupture and PMP.

Keywords: appendectomy; appendiceal mucinous neoplasm; cytoreductive surgery; extra-appendiceal mucin; hemicolectomy; intraperitoneal chemotherapy; pseudomyxoma peritonei.

Figure 1. Gross appendiceal specimen of Case 3 (1a-c). Appendix is grossly distended, with cut surfaces showing mucin-filled lumen. Specimens with LAMN, as in this case, can grossly present as dilated mucinous appendices. Pathology of this specimen showed LAMN.

LAMN, low-grade appendiceal mucinous neoplasm

Figure 2. CT abdomen and pelvis with contrast (Case 2). a) Axial view and b) coronal view showing a cystic lesion with peripheral calcification in the right abdomen. Subsequent exploratory laparotomy and appendectomy revealed a large cystic appendiceal tumor. Pathology of the lesion was consistent with LAMN.

LAMN, low-grade appendiceal mucinous neoplasm

Figure 3. CT abdomen and pelvis with contrast (Case 3). a) Axial view showing a cystic lesion in the right abdomen. b) Coronal view showing a RLQ tubular cystic mass with heterogeneous mural calcifications. Pathology of the mass showed LAMN.

RLQ, right lower quadrant; LAMN, low-grade appendiceal mucinous neoplasm

Figure 4. CT abdomen and pelvis with contrast (Case 5). Coronal view showing a cystic mass in the distal appendix. Pathological examination of the mass showed LAMN.

LAMN, low-grade appendiceal mucinous neoplasm

Figure 5. Algorithm for management of LAMN.

LAMN, low-grade appendiceal mucinous neoplasm

Figure 6. Pathology from Cases 1 to 5 (6a-e respectively).

Neoplastic mucinous epithelium grows along the hyalinized stroma and plunges through muscularis propria, consistent with pushing invasion. Lamina propria is scant or absent. Neoplastic epithelium shows low-grade dysplasia with nuclear pseudostratification (arrows). Usual features of infiltrative type invasion, such as single-cell invasion, desmoplastic stromal reaction, and tumor budding are absent.

Figure 7. A microphotograph shows mucin sitting on the serosa (yellow arrow), which reached there by dissecting the wall (red arrow shows subserosal adipose tissue - the outer wall of the appendix).