Dermoid cyst with a congenital sinus tract over the left sternoclavicular joint: a case report and literature review.

Dermoid cysts are rare benign tumors that arise from ectopic epiblastic inclusions and account for 0.4% to 1.5% of all tumors. They are usually 1 to 5 cm in size and composed of a pasty semisolid material. The orbital dermoid cyst is the most common type. Dermoid cysts can also occur in the spinal cord, ovaries, and pancreas. We encountered a 24-year-old man with a dermoid cyst over the left sternoclavicular joint. He reported intermittent secretion of a white tofu-like exudate from an underlying congenital sinus tract since birth. The secretion had turned hemorrhagic for the last month and had been accompanied by progressive swelling and pruritus for 1 week. Ultrasonography and magnetic resonance imaging revealed characteristics of a dermoid cyst, and histopathological examination confirmed the diagnosis. The patient underwent surgical excision of the cyst under local anesthesia. The incision healed well with no postoperative complications. Considering that a dermoid cyst has the potential to become infected or progress into squamous cell carcinoma, its removal at an early stage is suggested. Few reports in the literature have described a dermoid cyst that secretes hemorrhagic contents from a congenital sinus tract. We present this case to provide a reference for clinicians.