Tailgut cyst: CT and MRI findings

A 34-year-old female patient presented with complaints of occasional episode of lower-abdominal pain and constipation. Patient had no significant previous medical history. Clinical examination and routine investigations were done, all were normal. On per rectal examination bulge was palpated in right lateral wall.

Computed tomography (CT) showed well-defined irregular shaped hypodense cystic lesion in right pararectal and retrorectal space. It showed preserved fat plane with adjacent structures (Figure 1a).

On contrast enhanced CT (CECT), lesion didn’t show any enhancement (Figure 1b).

On Magnetic Resonance Imaging (MRI), lesion appeared iso-to hyperintense on T2-weighted image and hyperintense on T1-weighted and STIR image (Figure 2). It appeared hyperintense and did not show suppression on T1-weighted FATSAT image (exclude fat content) (Figure 3a). It didn’t show blooming artefact on T2-weighted GRE image (exclude haemorrhage within cystic lesion) (Figure 3b). Thus, confirming presence of mucinous or high protein content. It didn’t show restricted diffusion on Diffusion weighted Image (DWI) (exclude epidermoid cyst) (Figure 3c).

Final diagnosis of tailgut cyst with mucinous or high protein content was made.

Tailgut cyst is a rare congenital lesion occurring in retrorectal or presacral space. It is a remnant of tailgut which is distal most part of hindgut, which normally involutes by eighth week of embryonic life [1]. It is more common in female patients and can be discovered at any age, but usually presents in middle age [2].

Pathologically, tailgut cyst is multiloculated, cystic mass filled with mucoid material and has a thin wall lined by with multiple, various types of epithelium (predominantly columnar) [3].

It is usually detected incidentally but may present with abdominal pain or constipation [4].

Ultrasonography shows multilocular, retrorectal cystic lesion. Internal echoes may be present due to gelatinous material or inflammatory debris [4]. Computed tomography (CT) shows well-defined presacral mass with water or soft-tissue density, depending on the contents [4, 5]. Large mass displaces rectum [6]. In case of infection or malignant transformation it shows loss of discrete margins and involvement of adjacent structures [4].

On Magnetic resonance imaging (MRI), tailgut cyst may be unilocular or multilocular with internal septa. It appears hypointense on T1-weighted image (T1WI) and hyperintense on T2-weighted image (T2WI) [6, 7, 8]. However, due to presence of mucinous material, high protein content or haemorrhage, it may appear hyperintense on T1WI [7, 9]. In cases of malignant transformation, it shows irregular wall thickening or polypoid mass hypointense on both T1WI and T2WI post contrast enhancement [8, 9].

Histopathology provides definitive diagnosis of tailgut cyst [2].

Differential diagnoses of presacral cystic mass includes epidermoid cyst, dermoid cyst, rectal duplication cyst, anal gland cyst, cystic lymphangioma, and anterior meningocele [2].

Treatment is surgical excision [2].

Take home message: Though tailgut cyst is rare, it should be considered as differential diagnosis in presacral cystic lesion, and as it has malignant potential early diagnosis surgical removal is helpful.

Written informed patient consent for publication has been obtained.