Mucinous neoplasm of the appendix: A case report and review of literature

Abstract

Background: Appendiceal mucinous neoplasms (AMNs), although not classified as rare, are relatively uncommon tumors most often discovered incidentally during colorectal surgery. Accurate identification of AMNs is difficult due to non-specific symptoms, overlapping tumor markers with other conditions, and the potential for misdiagnosis. This underscores the urgent need for precision in diagnosis to prevent severe complications.

Case summary: This case report describes the unexpected discovery and treatment of a low-grade AMN (LAMN) in a 74-year-old man undergoing laparoscopic hemicolectomy for transverse colon adenocarcinoma (AC). Preoperatively, non-specific gastrointestinal symptoms and elevated tumor markers masked the presence of AMN. The tumor, presumed to be an AMN peritoneal cyst intraoperatively, was confirmed as LAMN through histopathological examination. The neoplasm exhibited mucin accumulation and a distinct immunohistochemical profile: Positive for Homeobox protein CDX-2, Cytokeratin 20, special AT-rich sequence-binding protein 2, and Mucin 2 but negative for cytokeratin 7 and Paired box gene 8. This profile aids in distinguishing appendiceal and ovarian mucinous tumors. Postoperative recovery was uncomplicated, and the patient initiated adjuvant chemotherapy for the colon AC.

Conclusion: This case highlights the diagnostic complexity of AMNs, emphasizing the need for vigilant identification to avert potential complications, such as pseudomyxoma peritonei.

Keywords: Adenocarcinoma; Appendiceal neoplasms; Case report; Low-grade appendiceal mucinous neoplasm; Peritoneal neoplasms; Pseudomyxoma peritonei.

Figure 1

Timeline of the initial diagnosis, surgical intervention, subsequent follow-up period, and adjuvant therapy.

Figure 2

Diagnostic imaging and interventions with the colonoscope. A: Colonoscopic examination revealed a 3-cm ulcerative lesion within the transverse colon, characterized by irregular luminal stenosis (white arrow); B: An attempt was made to obtain a biopsy through the colonoscope for pathological examination (white arrow).

Figure 3

Multistage intraoperative and specimen images of colonic adenocarcinoma and appendiceal mucinous neoplasm. A: Intraoperative photograph depicting the surgical field (white arrow); B: Comprehensive visualization of the adenocarcinoma and appendiceal mucinous neoplasm following an extended right hemicolectomy (white arrows); C: Image of the 6-cm neoplastic lesion located in the transverse colon (white arrow); D: Image of the 9-cm appendiceal mucinous neoplasm, featuring an intact capsular structure; E: Depiction of a large mucinous cavity within the appendix, which simulates a pseudo-diverticulum formation; F: The specimen submitted consists of one tissue fragment, measuring 10.6 cm × 4.0 cm × 3.3 cm in size, fixed in formalin. Grossly, it is opened and filled with mucoid materials.

Figure 4

Preoperative abdominal computed tomography image. A and B: The transverse colon wall and regional lymphadenopathy, correlating to a T3N1Mx stage, according to the 8^th edition of the American Joint Committee on Cancer cancer staging guidelines (orange arrow); C and D: A cystic formation approximately 9 cm in size was initially detected and interpreted as a mesenteric cyst; subsequent scrutiny ascertained it as an appendiceal mucinous neoplasm (orange arrow).

Figure 5

Preoperative coronal 2D Fast Imaging Employing Steady-state Acquisition magnetic resonance imaging of the abdomen revealed a cystic structure measuring approximately 9 cm in the right mesentery. The imaging was conducted with a 1.5 Tesla superconducting magnet and a phased-array body coil. The patient was positioned supine, with the imaging parameters set to a field of view of 40 cm, a slice thickness of 6 mm, and an interslice gap of 1.5 mm. This lesion was subsequently identified as an appendiceal mucinous neoplasm.

Figure 6

Histological examination of the lesion revealing characteristic patterns. A: A 200 × magnification image showing slender villi lined by tall mucinous epithelial cells with low-grade dysplasia; B: A 400 × magnification image demonstrating tall mucinous epithelial cells with low-grade dysplasia, set within a fibrous stromal framework; C: Immunohistochemical staining displaying positive CDX2 expression in the villous cells; D: Immunohistochemical staining displaying positive CDX20 expression in the villous cells; E: Immunohistochemical staining displaying positive SATB2 expression in the villous cells; F: Immunohistochemical staining displaying positive MUC2 expression in the villous cells; G: Immunohistochemical staining showing the villous cells negative for CK7; H: Immunohistochemical staining showing the villous cells negative for PAX8.Collective histopathological and immunohistochemical findings indicate the lesion to be a low-grade appendiceal mucinous neoplasm. The evaluation of surgical margins shows no neoplastic presence, indicating a clear disease-free status.

Figure 7

Treatment recommendations for appendiceal mucinous neoplasms (adapted from Govaerts et al[30] and Shaib et al[31]). LAMN: Low-grade appendiceal mucinous neoplasm; AMN: Appendiceal mucinous neoplasm; HAMN: High-grade Appendiceal Mucinous Neoplasm.