Tailgut cyst

Tail gut duplication cysts (TGC) or (also, also known as retrorectal cystic hamartomas) are, are rare congenital lesions that are thought to arise from vestiges of the embryonic hindgut. 

Epidemiology

There is an recognised strong female predilection. While it can present at any age presentation is usually at around 30-60 years of age ⁴.

Clinical presentation

Many lesions are discovered incidentally ⁵.  Approximately 50% of patients may have peri-rectal symptoms ^9,10.

Pathology

On grossly pathological examination, a tail-gut cyst usually comprises of a multiloculated, cystic mass with a thin wall and glistening lining and is filled with a mucoid material. The cysts can be lined by a variety of epithelial types, including ciliated columnar, mucin-secreting columnar, transitional, and squamous epithelium ¹⁰.

The lesions usually measure several centimeters in diameter. Occasionally a sacral bone defect and/or associated calcifications may be present ³. 

Location

It is almost exclusively found in the retrorectal or presacral space and very rarely in other locations such as the peri-renalperirenal area or in the subcutaneous tissues ⁷. 

Radiographic features

Ultrasound

Transrectal ultrasound

May be seen as a

CT

Often seen as a discrete, well-marginated, presacral mass with water or soft-tissue density, depending on the contents of the cyst. Calcifications may be seen in the cyst wall. When the mass is large, the rectum is displaced by the mass. If concurrent infection or malignant transformation occurs, CT may reveal loss of discrete margins and involvement of contiguous structures. 

MRI

MRI signal characteristics depend on whether the cyst is complicated or not. Complications include:

Uncomplicated

• T1:: low signal 
• T2 
  • high signal
  • some reports suggest that a multilocular appearance with internal septa on T2 images to cyst in the retrorectal being unique feature of to tail-gut cyst ⁶

Complicated cysts

• T1:: high signal components may occur due to the presence of mucinous material, high protein content, or associated intracystic haemorrhage. 
• T2:: low signal components may occur due to the presence of haemorrhage or associated Keratinkeratin ⁴

Complications

• infection or inflammation 
• malignant change is a rare and concerning potential complication ¹

Treatment and prognosis

While uncomplicated cysts are benign, surgical excision is the recommended treatment of choice even in asymptomatic cases, especially in view of potential complications ^3-5.

Differential diagnosis

General imaging differential considerations for a cystic lesion is the retro-rectalretrorectal region is rather broad and include ^3,8

• other developmental cysts in the retro-rectalretrorectal region
  • retrorectal epidermoid cyst
  • retrotectal dermoid cyst
  • retrorectal neurenteric cysts
• cystic sacrococcygeal teratoma
• anterior sacral meningocele
• anal duct cyst: anal gland cyst
• necrotic rectal leiomyosarcoma
• extraperitoneal adenomucinosis
• cystic lymphangioma in retrorectal region
• retrorectal pyogenic abscess
• necrotic sacral chordoma