Clinical Presentation of Low-Grade Appendiceal Mucinous Neoplasm (LAMN)
Typical Clinical Presentation
LAMN most commonly presents as acute appendicitis or is discovered incidentally during appendectomy, though some patients present with atypical symptoms such as isolated bloating and constipation rather than classic appendicitis symptoms. 1, 2
Common Presenting Features:
- Acute appendicitis symptoms are the most frequent presentation, making preoperative diagnosis challenging 1, 2
- Incidental discovery during appendectomy performed for suspected appendicitis is extremely common, as the disease lacks characteristic clinical symptoms 3, 4
- Palpable abdominal mass in the right lower quadrant may be present in some cases 3
- Asymptomatic presentation can occur, with the tumor remaining stable for extended periods 2, 5
- Bloating and constipation without classic appendicitis features have been reported 1
Critical Diagnostic Challenge:
The disease does not manifest a characteristic clinical profile, making it easy to misdiagnose without surgical intervention 3. Even when imaging is performed, misdiagnoses are common, highlighting limitations of preoperative diagnostic modalities 1.
Demographic Features
Age Distribution:
- Postmenopausal women and elderly patients are commonly affected, with reported cases in the 60s and 70s age range 1, 3
Sex Distribution:
- Both males and females are affected, though specific sex predominance data varies across case series 5
Tumor Characteristics at Presentation
Size:
- LAMN rarely exceeds 2 cm in diameter when confined to the appendix 4
- However, giant LAMNs have been reported, originating from the apex of the appendix and presenting as large mucoceles 3
Location:
- Tumors can originate from various parts of the appendix, including the apex 3
- Posterior positioning with adherence to the cecum represents an unusual intraoperative finding that may necessitate more extensive resection 1
Imaging Findings
Contrast-enhanced CT (CECT) is the imaging modality of choice, though discrepancies between CT and MRI findings are documented 1. The typical radiologic appearance is that of an appendiceal mucocele, though this finding is nonspecific 3, 4.
Critical Complications at Presentation
Pseudomyxoma Peritonei (PMP):
- Appendix perforation can lead to seeding of mucin and neoplastic epithelium into the peritoneum, causing PMP, a serious complication with high morbidity and mortality 2, 5
- Acellular mucin on the serosa is a significant risk factor for PMP development (p=0.004) 5
- T4b disease carries the highest risk of recurrence and PMP 5
Risk Factors for Progression:
- Appendix perforation (p<0.001) 5
- Presence of acellular mucin on serosa (p=0.004) 5
- Positive surgical margins 5
- T4a and T4b stage disease (p<0.001) 5
Pathologic Features at Diagnosis
Definitive diagnosis occurs through histopathological examination, typically after appendectomy, revealing villous or flat proliferation of epithelial lining, loss of lymphoid aggregates, and dissecting mucin within the muscularis 4. The National Comprehensive Cancer Network emphasizes that immediate histopathological classification is essential to determine the appropriate surgical approach 6, 7.