Dear Doctor: My brother told me he was having surgery to treat a pilonidal cyst. He told me that the condition was also called “pilonidal sinus disease.” What is pilonidal sinus disease? A pilonidal (pie-low-NIE-dul) cyst or sinus is an abnormal area or sack in the skin that usually contains dead skin, oil and debris. A pilonidal cyst is commonly situated near the … [Read more...]