A Case of Strangulation Ileus Due to a Low-Grade Appendiceal Mucinous Neoplasm

Background

Low-grade appendiceal mucinous neoplasm (LAMN) is a rare low-grade primary mucinous adenocarcinoma of the appendix as low-grade adenocarcinoma of the appendix according to current classification by the 2010 World Health Organisation (WHO) (2010) [1], the 2016 Peritoneal Surface Oncology Group International (PSOGI) modified Delphi classification [2]. Although LAMN is a low grade, slow-growing tumor, it has the potential for local spread to the peritoneum and rupture of the wall of the appendix followed by pseudo-myxoma peritonei (PMP) [3].

Early-stage LAMN is usually asymptomatic and is diagnosed incidentally on laparotomy, surgery, or abdominal imaging, as the presentation may mimic appendicitis [4]. When tumors are large, LAMN may be palpated as a right lower abdominal mass, or with abdominal pain due to intestinal obstruction or intussusceptions, or with intestinal bleeding, or PMP. Complete surgical resection is the most appropriate treatment for LAMN. A rare case is presented of strangulation ileus due to LAMN that presented as a surgical emergency in a 92-year-old man.

Case Report

A 92-year-old man was admitted to the emergency room with sudden onset of lower abdominal pain and abdominal distension. He had no previous history of abdominal surgery. On physical examination, his abdomen was distended, and he had generalized tenderness with mild guarding on palpation. Laboratory investigations showed mild anemia with a hemoglobin of 12.6 g/dl, a leukocytosis with a white blood cell (WBC) count of 14.6×103/μL with 85.5% neutrophils, blood urea nitrogen (BUN) of 26.6 mg/dL, a raised serum potassium of 5.1 mmol/L, and serum creatinine of 2.6 mg/dL, consistent with acute renal failure due to dehydration. Arterial blood gas analysis showed lactic acidosis (pH of 7.11) with a base excess of −20.8 mmol/L and lactate of 13.7 mmol/L.

Abdominal computed tomography (CT) showed ascites and a dilated obstructed closed loop of the distal ileum associated with an external mass (3.9×2.8 cm) (Figure 1). An initial diagnosis was of strangulation ileus due to Meckel’s diverticulum, and emergency surgery was performed. During laparotomy, 1.5 L of hemorrhagic ascites was drained. The distal ileum was dilated with ischemic change. The mesentery of the ischemic ileum was obstructed externally by the appendiceal mass in the space between the appendix and the mesentery of the terminal ileum (Figure 2).

Ileocecal resection with lymph node dissection was performed, based on the possibility of an appendiceal mucinous adenocarcinoma. The surgical resection specimen showed a 5.0×2.5 cm cystic tumor with mucus in the lumen (Figure 3A). Histopathology showed a columnar cell mucinous tumor without invasion or desmoplasia and with low-grade dysplasia of the neoplastic glandular cells (Figure 3B). There was no meta-static tumor in 17 resected regional lymph nodes. These findings supported a diagnosis of low-grade appendiceal mucinous neoplasm (LAMN). The diagnosis was made of strangulation ileus due to LAMN. The patient made a good postoperative recovery and was discharged home. Postoperative follow-up at 13 months showed no increase in serum tumor markers, including carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9), and no evidence of tumor recurrence.

Discussion

Low-grade appendiceal mucinous neoplasm (LAMN) is a rare tumor that is found in 0.2–0.3% of appendectomy specimens [7]. AMN was first described in 1940 by McDonald and Woodruff for a range of benign and malignant neoplasms arising in the appendix [8]. Subsequently, there have been several classification schemes [9–11], including the 2010 World Health Organisation (WHO) classification [1], and the 2016 Peritoneal Surface Oncology Group International (PSOGI) modified Delphi classification [2]. LAMN is characterized by low-grade dysplasia of the glandular epithelium, with or without mucin production. The histology of LAMN shows a villous tumor with expansive growth that may be associated with submucosal fibrosis involving the muscularis propria [1,2]. An important complication of LAMN is rupture through the wall of the appendix with the release of mucin into the peritoneum, or pseudomyxoma peritonei (PMP) [12]. In the early stage of the growth of LAMN, most patients have no symptoms, and the tumor is diagnosed incidentally during abdominal imaging or laparotomy for presumed acute appendicitis [4]. In larger tumors, patients may present with right lower quadrant abdominal pain, a palpable abdominal mass, weight loss, and change in bowel habit. Some patients also experience intestinal obstruction, intussusception, PMP, appendicitis, and localized appendiceal rupture due to LAMN [13].

Abdominal imaging has an important role in the diagnosis of LAMN and patient follow-up. Abdominal ultrasound may identify a cystic mass with mucinous content in the right lower quadrant of the abdomen [14]. Abdominal computed tomography (CT) may show a well-demarcated cystic mass in the appendix with low attenuation of the contents [15]. The cyst wall is usually smooth, with varying degrees of thickness, and calcification is present in up to 50% of cases [15]. Magnetic resonance imaging (MRI) of the abdomen may show hyperin-tense intraluminal fluid of the appendiceal cystic mass on T2-weighted imaging [16].

Intestinal obstruction is most commonly due to adhesions following surgery, or due to neoplasms, hernia, inflammatory bowel disease, intussusception, and volvulus. Intestinal strangulation caused by LAMN is extremely rare, with only a few cases reported in the literature [17,18]. Emergency surgery is the standard treatment for strangulated ileus due to LAMN, and complete resection with negative resection margins should be performed without spilling the contents into the peritoneum, which can result in PMP [19]. However, because LAMN is rare and may not be diagnosed preoperatively, and patients may present as a surgical emergency, surgical management remains controversial. In the case presented in this report, ileocecal re-section with regional lymph node dissection was performed due to the possibility of an appendiceal mucinous adenocarcinoma, the patient’s age, and the requirement to resect the ischemic terminal ileum.

Conclusions

This report is of a rare case of LAMN that presented as a surgical emergency with strangulation ileus in a 92-year-old man. This case has shown that although LAMN can be completely excised by surgical resection, its symptomatic presentation may be as a surgical emergency. In this case, accurate emergency pre-operative ant intra-operative evaluation was required during laparotomy with consideration of the patient’s age and their underlying medical condition. Because LAMN is a rare tumor, consensus management guidelines remain to be established.