A Low-Grade Appendiceal Mucinous Neoplasia and Neuroendocrine Appendiceal Collision Tumor: A Case Report and Review of the Literature

Abstract

BACKGROUND Incidental appendiceal neoplasms account for 1-2% of appendectomies. Mucinous neoplasms and carcinoids are the most frequent lesions, with an incidence of 0.6% and 0.3-0.9%, respectively. Appendiceal collision tumors are extremely rare and result from the proliferation of 2 different cellular lines. This report describes a young woman with a collision tumor composed of a low-grade appendiceal mucinous neoplasia (LAMN) and an appendiceal neuroendocrine tumor (ANET). CASE REPORT A 31-year-old woman was admitted to our institution presenting with abdominal pain and dysuria. After ultrasound assessment of a dilated appendix with wall thickening and distension by anechogenic material, a diagnosis of acute appendicitis was made. The patient, after a period of antibiotic therapy and observation, underwent an urgent laparoscopic appendectomy due to worsening condition. Surprisingly, the histological exam revealed a Tis LAMN extending from the base of the appendix to the resection margins, and a T3 grade-1 ANET, chromogranin-A and synaptophysin-positive, with a Ki67 less than 1%. On the basis of histological examination and European Neuroendocrine Tumor Network guidelines, in light of the positive LAMN resection margin and ANET mesoappendiceal invasion, after multidisciplinary team discussion, an elective laparoscopic hemicolectomy was indicated. The patient is now in good condition following a regular 5-year follow-up. CONCLUSIONS A collision LAMN and ANET is an exceedingly rare condition. The heterogeneity of clinical presentation and lack of solid evidence seem to recommend a tailored management. Laparoscopy is a safe and useful tool in localized mass excision.

Figure 1.

Abdominal ultrasound showing an appendix 5.5 cm long, dilated, and distended by an anechogenic material with wall thickening.

Figure 2.

(A) H&E, 10×: Neuroendocrine tumor, grade 1 (carcinoid) at tip. Large and small nests composed of polygonal cells with salt-and-pepper chromatin and cytoplasmic brightly eosinophilic basally-located granules (insert; H&E 200×). Muscularis propria and subserosal tissue were infiltrated. In immunohistochemistry analysis (not shown), these cells were positive for chromogranin-A and synaptophysin. No mitosis was observed, and the Ki-67 proliferation index was less than 1%. (B) H&E 10×, and (C) H&E 100×: Low-grade appendiceal mucinous neoplasms (LAMN). At the corpus, the lumen was dilated by mucus accumulation. Mucosa-associated lymphoid tissue was absent. The normal mucosa was replaced with an undulating epithelial monolayer of uniform columnar cells with apical mucin and basal hyperchromatic nucleus. Muscularis mucosae were maintained. (D) H&E 10×. On subsequent right hemicolectomy, the specimens showed a residual appendix partially occluded by extensive fibrosis. The lumen was filled with acellular mucus. In the caecum wall there was a lake of extracellular mucus in the submucosa without evidence of epithelial cells.