Differential Diagnosis for a Cyst at the Top of the Butt Crack

• Single most likely diagnosis
  • Pilonidal cyst: This is the most common diagnosis for a cyst located at the top of the butt crack, also known as the natal cleft. Pilonidal cysts are typically filled with hair and skin debris, and can become infected, leading to abscess formation.
• Other Likely diagnoses
  • Epidermoid cyst: These are benign cysts that can occur anywhere on the skin, including the natal cleft. They are usually filled with a thick, cheesy material and can become infected.
  • Furuncle or carbuncle: These are infections of the hair follicles, which can occur in the natal cleft and present as a cyst or abscess.
  • Hidradenitis suppurativa: This is a chronic skin condition that can cause cysts and abscesses in the apocrine-gland-bearing areas of the body, including the natal cleft.
• Do Not Miss diagnoses
  • Anal fistula: Although less common, an anal fistula can present as a cyst or abscess in the natal cleft. It is a connection between the inside of the anus and the skin, and can be a sign of a more serious underlying condition, such as Crohn's disease.
  • Rectal cancer: Although rare, rectal cancer can present as a cyst or mass in the natal cleft. It is essential to rule out this diagnosis, especially in older adults or those with a family history of colorectal cancer.
• Rare diagnoses
  • Teratoma: This is a rare type of tumor that can occur in the natal cleft. It is usually present at birth and can contain hair, teeth, or other tissues.
  • Dermoid cyst: This is a rare type of cyst that can occur in the natal cleft. It is usually present at birth and can contain skin, hair, and other tissues.
  • Tuberculosis: Although rare in developed countries, tuberculosis can cause cysts and abscesses in the natal cleft, especially in immunocompromised individuals.