Umbilical pilonidal sinus.

Although most cases of pilonidal sinus occur in the sacrococcygeal region, umbilical presentations can occur. Due to risk of peritoneal extension of inflammation from this lesion, the umbilical pilonidal sinus should be treated more aggressively than its sacrococcygeal counterpart. Pilonidal sinus should therefore be included in the differential diagnosis of umbilical nodules.