A pilonidal cyst is a sac under the skin at the base of the spine. It can become infected.Â When it does the physician will use a scalpel to excise the adjacent tissue. Code selection is based on whether the excision of the cyst is simple, extensive, or complicated. A simple excision (11770 Excision of pilonidal cyst or sinus; simple) is closed in only one layer. If several layers of closure are required and the documentation indicates extensive or complicated; turn to 11771 Excision of pilonidal cyst or sinus; extensive or 11772 Excision of pilonidal cyst or sinus; complicated. In 11771 an extensive sinus, greater than 2 cm, is present superficial to the fascia overlying the sacrum, or there are extensions. The cystic tissue is excised and sutured in several layers. In 11772 the sinus may be infected and involves many subcutaneous extensions, which are excised. Local soft tissue flaps may be required for closure of a large defect.