Cause of an acute abdomen never seen: Intraabdominal perforation of an umbilical pilonidal sinus abscess.

Pilonidal sinus is a well-known disease of the sacrococcygeal region, which is caused by hair shafts penetrating the epidermis. The granulomatous reaction is the characteristic of this chronic inflammatory disease. Umbilical pilonidal sinus is an acquired disease that may appear in many guises and mimic several umbilical conditions. Several risk factors for developing the disease have been described. Treatment is based on clinical experience rather than on evidence-based medicine. The umbilical pilonidal sinus, which is not treated medically or surgically, may cause regional or generalized infections. We suggest that our case which has never had symptoms before and has caused acute abdomen, will be considered in the diagnosis of acute abdomen.