A rare case of tailgut cyst associated with Currarino’s syndrome

A 2-year-old female child, previously managed with descending colostomy for low anorectal malformation was brought for routine follow-up. There was no history of abdominal pain or constipation. Her colostomy stoma was functional. On clinical examination, a pelvic mass was palpable incidentally. Neurological examination was normal.

Anteroposterior pelvic radiograph showed partial sacral agenesis with a right-sided defect.

On ultrasound examination, a multiloculated cystic mass with internal septations was seen in the pelvis.

MRI was done to characterize the mass and for surgical planning. The multilocular cyst had variable signal intensities on T1WI and high signal intensity on T2WI. The cyst was noted communicating with the spinal canal, however, no continuity with thecal sac was demonstrated.

Non-Enhanced Computed Tomography (CT) was performed to review in detail the bony changes. Partial agenesis of the sacrum was noted, and the three-dimensional volume rendering depicted the classical appearance of “Scimitar sacrum”. There was no evidence of calcification, fat or solid component within the presacral mass. Communication of the mass with the spinal canal was noted through the bony defect.

CT also showed left gross hydroureteronephrosis. There was neither abrupt tapering of the ureter suggestive of a stricture nor extrinsic compression by the mass. A micturating cystourethrogram was not performed to look for vesicoureteral reflux.

The presacral mass was excised, tissue diagnosis was tailgut cyst (retrorectal cystic hamartoma). Histopathology showed cysts lined by stratified squamous, ciliated columnar and transitional epithelium with intervening areas of fibromuscular tissue.

Currarino syndrome (CS) was described as a triad by Guido Currarino, an American radiologist in 1981. It is a complex condition characterised by partial sacral agenesis, anorectal malformation and presacral mass [1]. The latter can be a teratoma, anterior sacral meningocele, enteric cyst or a combination of these. The triad is often incomplete with only 1 out of 5 cases presenting with all three abnormalities.

The cause for most of the cases is haploinsufficiency of the gene MNX1 (Motor neuron and pancreas homeobox 1) on 7q36 that plays a role in the dorsoventral separation of the caudal embryo [2]. The defect may be sporadic or inherited as an autosomal dominant trait with variable penetrance. When inherited, it is most frequently transmitted in the female line.

Bowel obstruction in infancy or chronic constipation in childhood are the commonest presenting symptoms [3]. About 60% of patients have associated occult spinal dysraphism.  Müllerian duct anomalies such as bicornuate or septate uterus and rectovaginal fistula have been associated in up to 15% of cases [4]. Genitourinary associations include horseshoe or duplex kidney, vesicoureteral reflux, neurogenic bladder, urinary incontinence and hydronephrosis [5].

Pelvic MRI is the gold standard for the diagnosis of presacral mass, delineation of the anatomic extent of the tumour and tissue characterization. It also helps in detecting the communication between the anterior sacral meningocele and the spinal subarachnoid space [6]. It also serves as a useful tool for assessing the level of the rectal pouch and sphincteric muscle development in anorectal malformations (ARM). In our case, ARM was previously corrected with descending colostomy.

Sacral bony defects are better visualized with a CT scan. The sacrum is partially deficient and often assumes a scimitar shape that results from a unilateral deficiency of S2-S5 with an intact S1 vertebra [7].

Tailgut cysts are quite rare and are thought to be derived from remnants of the primitive hindgut. They typically present as retrorectal cystic masses, frequently multilocular, hypointense on T1WI (signal intensities can vary depending on the protein content of the fluid) and hyperintense on T2WI. These imaging features are similar to the findings in our case. Lack of communication with the thecal sac and lack of fat component rules out anterior sacral meningocele and teratoma respectively.

The presacral tumours associated with Currarino’s triad tend to behave differently from other sacrococcygeal tumours. There is a low risk of malignant transformation compared with the latter.

Written informed patient consent for publication has been obtained.