JRSM >
Volume 94, Number 7 >
Pp. 353-354
Department of Surgery, Luton and Dunstable Hospital, Luton LU4 0DY, UK
Correspondence to: S L Khan E-mail: sumaira{at}khan48.fsnet.co.uk
Large intra-abdominal cystic masses can be difficult to diagnose preoperatively. Imaging with ultrasound and computed tomography is sometimes deceptive.
CASE HISTORY
A previously fit man of 34 was admitted after two days of sudden-onset lower abdominal pain, nausea and vomiting. He had no other associated symptoms. On examination, he was tender to palpation across the lower abdomen, with dullness to percussion in the suprapubic area which persisted despite urinary catheterization. Full blood count, urea and electrolytes and urinalysis were all normal. An abdominal X-ray showed a calcified mass in the pelvis. Abdominal ultrasound revealed a well-defined mass measuring 12.5 x 7 x 7 cm in the central lower abdomen and pelvis, reported as ‘resembling abnormal bowel’. His symptoms settled with conservative management and he was discharged pending further investigation.
A CT scan showed a 10 x 5 cm tubular cystic structure with rim calcification between the sigmoid colon and rectum, indenting the bladder but not communicating with it. The appearances were reported as compatible with an enteric duplication cyst (Figure 1). On review in the outpatient clinic, the patient complained of discomfort in the lower abdomen and dysuria. A large suprapubic mass was now palpable. A contrast magnetic resonance scan of the pelvis, performed to determine the relationship of the cyst to the surrounding vasculature, revealed a unilocular lesion with morphology more suggestive of a mesenteric cyst than of an enteric duplication cyst, non-pancreatic pseudocyst or lymphangioma (Figure 2).
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In view of the continued symptoms and the diagnostic uncertainty, the patient was admitted for a laparotomy and excision of the pelvic mass. At operation, a unilocular thick-walled swelling was found filling the pelvis, adherent to the bladder anteriorly, the rectum posteriorly, and the right ureter laterally. It was dissected off each structure without injury, and on being lifted out of the pelvis was seen to be arising from the caecal pole; an appendicectomy was therefore performed. The excised mass was a sausage-shaped, well-circumscribed cream and pink tumour measuring 21 x 7 x 8 cm with a fibrous wall. The cavity contained thick yellow and cream mucus. Histological features were those of a mucocele of the appendix with no evidence of atypia or malignancy.
COMMENT
Mucocele of the appendix was first described by Rokitansky in 1842 and named by Fere in 18761. The term is used to describe a cystic mass resulting from a dilated appendiceal lumen containing large quantities of mucus and occasionally associated with mucinous intraperitoneal collections2. It is a rare condition with an incidence of between 0.07% and 0.3% in appendicectomy specimens1. It tends to be more common in females, though one series review showed a slight male preponderance3.
Mucoceles are divided into four types according to the nature of the epithelial lining of the appendix: (a) simple mucocele due to obstruction of outflow, for example by a faecolith (the most common type); (b) mucoceles with mucosal hyperplasia; (c) mucinous cystadenomas where the epithelial lining is characterized by villous adenomatous change, with or without atypia of the cells; and (d) malignant mucinous cystadenomas in which the epithelium exhibits ‘glandular stromal invasion’ and peritoneal deposits may contain malignant epithelial cells2,4. The usual mode of presentation is with right lower quadrant pain or intermittent colicky lower abdominal pain; however, about a quarter of all diagnosed mucoceles are discovered incidentally at operation3.
Preoperative diagnosis is important because, if the lesion is due to cystadenoma or cystadenocarcinoma of the appendix, rupture may produce the potentially fatal condition of pseudomyxoma peritonei3. The presence of malignant disease also has implications for the necessary extent of bowel resection during surgery and future treatment and prognosis.
Ultrasound and CT scan are useful diagnostic tools in both mesenteric cysts and appendix mucoceles. On ultrasonography, mesenteric cysts tend to appear as cystic structures, usually with internal septations; whereas mucocele of the appendix has variable internal echogenicity according to content. The wall may consist of a thin inner rim and an outer layer representing bowel. On CT, a thick wall may signify the presence of atypia or malignancy in a mucocele3,5. Mural calcification in a mucocele is a rare but well recognized radiological finding. It is usually patchy but may be seen as a semicontinuous rim6. Calcification was visible in our patient's abdominal X-ray and CT scan and may be an important distinguishing factor between cysts and mucoceles.
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