A tailgut cyst is a rare developmental lesion and usually is located in the retrorectal or presacral space. Extrahepatic hydatid disease has been reported in several locations including the pelvis and it often poses a diagnostic challenge. There are very few reported cases of primary perineal hydatid cysts. We present the multimodality imaging findings of a tailgut cyst and concurrent perineal hydatid disease in a 32-year-old male patient.
A tailgut cyst is a rare congenital lesion. It has a female predilection and is usually asymptomatic and detected during middle age [
Hydatid disease is a zoonotic parasitic disease.
A 32-year-old male patient with a history of poliomyelitis in childhood complained of a progressively enlarging painless deep perianal mass for 1 year with a history of intermittent chronic constipation. The patient was referred to a tertiary healthcare center as a possible case of retroperitoneal sarcoma. Routine contrast enhanced CT showed a large (7.2
Multiple axial and sagittal contrast enhanced CT scan show a multilocular, hypoattenuating, retrorectal cystic lesion (asterisks) displacing the rectum (R) anteriorly. The left ischioanal fossa cystic lesion (solid arrow) shows enhancing wall and internal septations, breaching the left levator ani muscle and extending into the left perineal subcutaneous fat (dashed arrow). Atrophy of the right hemipelvis and proximal thigh muscles is noted and related to known poliomyelitis.
Fused FDG PET/CT images show no FDG uptake in the known retrorectal tailgut cyst (solid arrow) or the left ischioanal and perineal subcutaneous hydatid cysts (dashed arrows).
Pelvic magnetic resonance imaging (MRI) was performed. The retrorectal mass showed intermediate signal intensity on both T1 and T2 with multiple internal T1 hypointense foci and T2 hyperintense foci. The left ischioanal fossa collection of cysts showed low T1 and high T2 signal intensity with multiple internal cysts and T2 and T1 hypointense rim. There was thin peripheral enhancement with no enhancing mural solid component. There was no osseous involvement (Figure
(a) Sagittal T2-weighted MR image with fat saturation shows a predominantly intermediate T2 signal intensity presacral/retrorectal multilocular lesion (asterisk) with multiple internal T2 bright foci and smaller peripheral cysts (arrowheads). Note the anterior displacement of the rectum. The left ischioanal (solid arrow) and subcutaneous perineal hydatid cysts (dashed arrow) show high T2 signal intensity with dark internal septations and rims. (b) Sagittal T1-weighted postcontrast MR image shows peripheral rim enhancement of the retrorectal tailgut cyst (asterisks) as well as the ischioanal (solid arrow) and perineal subcutaneous hydatid cysts (dashed arrow). ((c) and (d)) Axial T2-weighted (c) and T1-weighted (d) MR images show the retrorectal lesion of intermediate signal intensity (asterisk) with peripheral small cyst. ((e) and (f)) Axial T2-weighted (e) and T1-weighted (f) MR images show the left subcutaneous perineal hydatid cysts (dashed arrow) of high T2 signal intensity and intermediately low T1 signal intensity with internal daughter cysts and a dark rim.
The patient underwent surgical resection. The histopathologic examination of the resected retrorectal cyst revealed a benign tailgut cyst. The resected left ischioanal and gluteal cystic lesions showed an outer histiocytic reaction to a hydatid cyst.
The unique feature of this primary extrahepatic hydatid cyst is its very unusual location in the ischioanal fossa with extension to the left perianal and gluteal areas. While the hydatid cysts had increased signal on T2-weighted images, the tailgut cyst had intermediate signal, denoting proteinaceous or mucinous content. The presence of both a perineal hydatid cyst and tailgut cyst with differing signal characteristics on MRI in a contiguous location in one patient imposed a diagnostic challenge where the added information of MRI proved very useful. In fact, the interpreting radiologist suggested a developmental lesion such as a tailgut cyst and atypical hydatid disease. The differential diagnosis might include a myxoid tumor such as myxoid neurofibroma or aggressive angiomyxoma due to the presence of myxoid, proteinaceous, or mucinous contents. However, the lack of an enhancing solid component makes those diagnoses less likely.
A tailgut cyst is a rare developmental lesion that is a remnant of the embryonic tailgut. The tailgut is the most caudal part of the hindgut that normally involutes during embryonic development. Tailgut cysts have a female predilection, are usually asymptomatic, and are often detected in middle age. They can be discovered at any age and may cause symptoms such as abdominal pain or constipation [
The imaging findings of tailgut cysts on CT and MRI have been described. Usually, CT shows a presacral, discrete, and well-marginated lesion of fluid or soft tissue attenuation depending on the cyst contents. Cyst wall calcifications may be seen and the rectum may be displaced if the lesion is large [
Because of the malignant potential of a tailgut cyst, to distinguish it from the other presacral cysts is essential. Differential diagnoses of a presacral cystic lesion might include rectal duplication cyst, dermoid cyst, epidermoid cyst, cystic lymphangioma, and anterior meningocele. These diagnoses are usually unilocular except for a tailgut cyst and cystic lymphangioma which are usually multicystic [
In humans, hydatid disease affects the liver, the lung, and other locations in approximately 75%, 15%, and 10% of cases, respectively [
Hydatid disease has a variable imaging appearance. There is a standardized WHO classification of the hydatid cyst stages based on the Gharbi ultrasound classification [
Stojkovic et al. compared the MR and CT imaging findings with ultrasound and concluded that the hydatid cyst matrix is the main defining feature of cyst stage. Also, the “double line sign” is diagnostic for hydatid stage 1. The cyst wall calcifications play some role in defining cyst stage 5 which may be challenging on MRI. Therefore when compared to ultrasound, MRI performs very well with WHO hydatid cyst stages 1, 2, 3, and 4. T2-weighted MR images provide the best sequence to detect cyst contents, that is, septa (stage 2) and daughter cysts (stage 3b) [
While a tailgut cyst is a rare entity, it should be considered when there is a presacral multilocular mass. Hydatid disease may affect any part of the human body and often has nonspecific imaging findings and serological tests are not always positive. The simultaneous contiguous occurrence of both diagnoses is rare. Attention to the unique imaging features of each cystic lesion facilitates the diagnosis. Clinicians and radiologists should entertain hydatid cysts in their differential diagnoses whenever they encounter cystic lesions especially if the patient is from an endemic area.
The authors declare that they have no competing interests.