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Tail gut duplication cyst

A tail gut duplication cyst (TGC) or retrorectal cystic hamartoma is a rare congenital lesion which is thought to arise from vestiges of an 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 retro-rectal or pre-sacral space and very rarely in other locations such as the peri-renal area or in the subcutaneous tissues 7

Radiographic features

Trans rectal ultrasound

May be seen as a multi-locular, retro-rectal 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-sacral 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 gut cyst usually has the following signal characterisitcs

  • T1 : low signal 
  • T2
    • high signal
    • some reports suggest that a multi-locular appearance with internal septa on T2 images to cyst in the retro-rectal being unique feature of to tail gut cyst 6
Complicated cysts
  • T1 : high signal components : can occur due to the presence of mucinous material, high protein content, or associated intracystic haemorrhage. 
  • T2 : low signal components : can occur due to the presence of haemorrhage or associated Keratin 4

Complications

  • infection or inflammation 
  • associated malignant change : a rare a 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

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