Tailgut cyst

A tailTail gut duplication cystcysts (TGC) or (also known as retrorectal cystic hamartomahamartomas is a) are rare congenital lesion which islesions that are thought to arise from vestiges of anthe embryonic hindgut. 

Epidemiology

There is an recognised strong female predilection While it can present at any age presentation is usually at around 30 - 60-60 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-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/or associated calcifications may be present ³. 

Location

It is almost exclusively found in the retro-rectalretrorectal or pre-sacralpresacral space and very rarely in other locations such as the peri-renal area or in the subcutaneous tissues ⁷. 

Radiographic features

Trans rectalTransrectal ultrasound

May be seen as a multi-locularmultilocular, retro-rectalretrorectal cystic mass. Internal echoes may be found within the cyst due to the multi-cystic nature of the mass and the presence of gelatinous material or inflammatory debris within the cyst. 

CT

Often seen as a discrete, well-marginated, pre-sacralpresacral 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

On MRI, an uncomplicated tail gutMRI signal characteristics depend on whether the cyst usually has the following signal characterisitcsis complicated or not.

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

Complicated cysts

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

Complications

• infection or inflammation 
• associated malignant change :is a rare aand 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-rectal region is rather broad and include ^3,8

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