Appendiceal mucocele : An unusual cause of lower back pain

Clinical History

A 52-year-old man was referred to the emergency department. His complaints were lower back pain radiating to McBurney's point with nausea. The symptoms started 7 days prior. When palpating the lower right quadrant of the abdomen the patient felt pain, muscles were moderately rigid, without rebound tenderness on palpation. Body
temperature was 37, 5°C. Laboratory tests showed leucocitosis (11000 GB/µL).

Imaging Findings

Ultrasound showed a tubular fluid-filled mass with hypoechogenic and homogeneous contents in the right lower quadrant of the abdomen (figure 1). The mass was suspicious for appendiceal mucocele, and the patient underwent a CT of the abdomen and pelvis that showed a 10x3x3cm in diameter, blind-ending, tubular, fluid-filled structure appearing to arise from the cecum (figure 2), arriving posterior next to the lower pole of the right kidney (figures 3, 4), without infiltration of the mesenteric fat or nodes, consistent with mucocele of the appendix .

Discussion

Appendiceal mucocele is a rare but well-recognized entity that can mimic several common clinical syndromes or present as an incidental surgical or radiological finding. It has a 0.2% to 0.4% prevalence among appendectomies [1, 2]. The size of the mucocele is highly variable, ranging from a few centimeters to very large masses up to 40 cm. The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus [3], resulting from chronic appendiceal obstruction caused either by benign or malignant lesions. In fact, 12% to 36% of mucoceles are caused by adenocarcinoma [4]. Although preoperative diagnosis by means of imaging techniques is advisable for better surgical planning (careful handling avoids dissemination of mucoid implants throughout the peritoneum, and suspected malignancy imposes a right hemicolectomy), mucoceles are hardly ever identified before surgery (<20% of cases, on average). The presentation of appendiceal mucoceles is quite variable. Acute appendicitis from luminal obstruction is the most common manifestation. Approximately 25% of mucoceles are asymptomatic [5]. Our patient had an atypical symptomatology since her mucocele was developing in posterior and because of the distension of its distal end that came in proximity of the kidney. Ultrasound findings can be variable: purely cystic lesions with anechoic fluid, hypoechoic masses with fine internal echoes as well as complex hyperechoic masses can be seen depending on the contents. The onion skin sign (sonographic layering within a cystic mass)is considered to be specific for mucocele of the appendix [1]. On CT, appendiceal mucocele is typically seen as a well-circumscribed, low-attenuation, spherical or tubular mass contiguous with the base of the caecum. The finding of curvilinear mural calcification suggests the diagnosis, but is seen in less than 50% of cases [6], intra-luminal bubbles of gas, or an air-fluid level within a mucocele suggest the presence of superinfection, which can occur in both benign and malignant mucocoeles. As reported by some authors, soft-tissue thickening, wall irregularity, and periappendiceal fat stranding are nonspecific findings that can indicate malignancy, secondary inflammation, or both [7]. The definitive diagnosis depends on pathology; surgical resection is preferred to observation due to the potential for malignant transformation and dissemination. A recent literature review recommended that an open approach is generally preferred over laparoscopy to reduce the risk of iatrogenic perforation [8]. The prognosis of a benign appendiceal mucocele after treatment is good, with a 5-year survival rate of 91-100%. For malignant lesions, this drops to 25% at five years, usually due to complications from pseudomyxoma peritonei [9].

Differential Diagnosis List

Final Diagnosis

appendiceal mucocele without individualization of malignancy suspicious cells

URL:	https://www.eurorad.org/case/13126
DOI:	10.1594/EURORAD/CASE.13126
ISSN:	1563-4086