Urachal Remnant Abscess

Case History: An 18-year-old boy presented to the surgery outpatient clinic with a one-week history of a painful swelling at the umbilicus with purulent discharge.

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FIGURE 1
Ultrasound revealed a bilobed cystic lesion under the umbilicus with echogenic contents in the umbilical cleft and relatively hypoechoic contents in the deeper component of the collection (Fig1).

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FIGURE 2
A contrast CT of the abdomen revealed a lobulated collection under the umbilicus with thick marginal enhancement (Fig 2).

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FIGURE 3
The posterior margin of the collection was closely applied to the urachus which showed mild focal thickening and enhancement (Fig 3).[[{"type":"media","view_mode":"media_crop","fid":"17441","attributes":{"alt":"","class":"media-image","id":"media_crop_8956586225","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"973","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","title":" ","typeof":"foaf:Image"}}]]

FIGURE 4
Rest of the urachus was best visualized on sagittal reformatted images as a thin isodense cord extending from the umbilical collection till the bladder vault (arrowed in Fig 4).

Diagnosis: Urachal remnant abscess

An imaging diagnosis of an urachal abscess draining through the umbilicus was made, most likely due to an infected urachal cyst. The patient was treated with surgical drainage under antimicrobial cover followed by complete excision of the cyst. Total removal of the cyst wall is essential to avoid reinfection. Reinfection rates are as high as 30 percent in incompletely treated cases.

The urachus is a fibrous cord extending from the bladder vault till the umbilicus and is the vestigial remnant of the urogenital sinus and allantois. Persistence of all or part of the urachus can result in congenital or acquired urachal remnant diseases. Congenital urachal remnants may present as a patent urachus (50 percent), umbilical-urachal sinus (15 percent), vesicourachal diverticulum (3 percent to 5 percent) or an urachal cyst (30 percent) (Fig-5 - Courtesy reference 3 below)

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FIGURE 5

Acquired remnant disorders are mainly due to infection or neoplasm. Infection within an urachal cyst is uncommon with a peak incidence in infancy and then again in early adulthood. The adult presentation may be a consequence of partial opening of the urachus which may have closed at birth. Direction of drainage of infected urachal fluid depends on the type of urachal patency. Umbilical urachal sinuses and infected cysts close to the abdominal wall will result in umbilical discharge. Infected cysts close to the bladder and vesico-urachal diverticuli may present with urinary symptoms. Uncommonly, a large infected cyst may rupture into the peritoneal cavity and cause peritonitis.

Ultrasound and CT are both reliable modalities for diagnosis of urachal abscess. Demonstration of a midline fluid containing structure within the anterior abdominal wall and extension into the umbilicus with or without umbilical discharge is virtually diagnostic of a urachal abscess. In some complex abscesses, the mixed echoes on USS and heterogeneous enhancement on CT may mimic a urachal carcinoma and an image guided FNAC or biopsy is then indicated for definitive diagnosis and therapeutic planning.

Arti Chaturvedi MD
Senior Consultant, Department of Radiodiagnosis
Fortis International Hospital, Noida, India

References:
1. Yu JS, Kim KW, Lee HJ, Yoon CS, Kim MJ. Urachal Remnant Diseases: Spectrum of CT and US Findings. Radiographics March 2001; 21: 451-461.
2. Walker C A Case Report of Urachal Abscess: A Rare Differential in Adult Abdominal Pain. Hawaii Med J. 2010 February; 69(2): 35–36.
3. Abscess of urachal remnants presenting with acute abdomen: a case series. Tazi F, Ahsaini M, Khalouk. Journal of Medical Case Reports Journal of Medical Case Reports 2012, 6:226 doi:10.1186/1752-1947-6-226
4. Ash A, Gujral R, Raio C. Infected urachal cyst initially misdiagnosed as an incarcerated umbilical hernia. J Emerg Med. 2012 Feb; 42(2):171-3.