Urachal abscess mimicking malignant tumor: can imaging tell them apart?

Abstract

The urachus is an embryonic remnant that usually involutes before birth. Abnormal persistence of this structure can lead to infectious or neoplastic complications later in life. We report a case of an 84-year-old man that presented with a urachal complex mass which, after proper investigation, revealed to be a urachal abscess. Urachal abscesses are rare and usually occur in severe infections. Urachal abscesses can be indistinguishable from urachus carcinoma on imaging studies. This article reviews the clinical and imaging aspects of urachal abscess and carcinoma and possible differentiating elements in imaging. However, definitive diagnosis usually depends on a biopsy or fluid aspiration.

Keywords: Abdomen/GI; abscess; biopsy; embryonic remnants; urachus.

Fig. 1.

Axial pelvic US image, with the probe at the midline, showing an anterior ill-defined, complex heterogeneous mass (blue arrows) with a hypoechoic center, suggesting cystic/fluid nature, and a mixed hypo and hyperechoic appearance at the periphery, suggesting a solid component.

Fig. 2.

Sagittal (a) and axial (b) enhanced CT images showing a 9 × 4.5 cm oval mass (blue arrows) with thick irregular enhancing peripheral wall and central non-enhancing low attenuation area (star) located in the lower abdomen, between the umbilicus (red arrow) and the bladder (green arrow). The sagittal image (a) shows that the lesion is in continuation with the urinary bladder caudally (thin arrow).

Fig. 3.

Biopsy area (stained with hematoxylin and eosin) showing inflammatory tissue with lymphocytes, plasmocytes, macrophages, new capillary vessels, and fibroblasts.

Fig. 4.

Biopsy area (stained with Masson trichrome) showing dense fibrosis with fascicles of collagen and spindle fibroblasts, and a few small blood vessels.

Fig. 5.

Sagittal (a) and axial (b) enhanced follow-up CT images showing almost complete resolution of the mass, persisting an enhancing cord-like structure (blue arrow) between the umbilicus (red arrow) and the bladder (green arrow).