Spinal dermal sinus

May appear as a dimple or as a sinus, with or without hairs, usually very close to midline, with an opening of only 1–2mm. Surrounding skin may be normal, pigmented (“port wine” discoloration), or distorted by an underlying mass.

The sinus may terminate superficially, may connect with the coccyx, or may traverse between normal vertebrae or through bifid spines to the dural tube. It may widen at any point along its path to form a cyst; called an epidermoid cyst if lined with stratified squamous epithelium and containing only keratin from desquamated epithelium, or called a dermoid cyst if also lined with dermis (containing skin appendages, such as hair follicles and sebaceous glands) and also containing sebum and hair.

Although innocuous in appearance, they are a potential pathway for intradural infection which may result in meningitis (sometimes recurrent) and/or intrathecal abscess. Less serious, a local infection may occur. The lining dermis contains normal skin appendages which may result in hair, sebum, desquamated epithelium and cholesterol, within the tract. As a result, the contents of the sinus tract are irritating and can cause a sterile (chemical) meningitis with possible delayed arachnoiditis if it enters the dural space.

Incidence of a presumed sacral sinus (a dimple whose bottom could not be seen on skin retraction): 1.2% of neonates