Postanal dermoid

Postanal dermoid

The space in front of the lower part of the sacrum and coccyx may be occupied by a soft, cystic swelling – a postanal dermoid - cyst. Hidden in the hollow of the sacrum it is unlikely to be discovered unless a sinus communicating with the exterior is present or it develops as a result of inflammation. Such a cyst usually remains asymptomatic until adult life, when it is prone to becoming infected. Exceptionally , because of its size, it gives rise to di ffi culty in defecation. The cyst is easily palpable on - rectal examination. Differential diagnosis An anterior sacral meningocele must be excluded, particularly in the presence of bony abnormality of the sacrum. This enlarges when the child cries and is frequently associated with paralysis of the lower limbs and incontinence. When a discharging sinus is present, a postanal dermoid will probably - be mistaken for a pilonidal sinus or even an anal fistula. Pressure over the sacrococcygeal region with a finger in the rectum may cause a flow of sebaceous material, and injection of contrast medium followed by radiography reveals a bottle-necked cyst in front of the coccyx. Treatment Treatment involves complete excision of the cyst and, if present, the sinus. In the case of large cysts, it is necessary to remove the coccyx to gain access. The coccyx should also be removed en - bloc in any child with a presacral dermoid because of the risk of sacrococcygeal teratoma. Care must be taken to exclude the Currarino triad, an autosomal dominant hereditary condition characterised by sacral malformation, anorectal malformation (often stenosis) and a presacral mass consisting of a dermoid cyst/teratoma and/or anterior meningocele.