Trichodermal cyst

This code identifies a trichilemmal cyst, a common benign epidermal cyst originating from the outer root sheath of a hair follicle. These cysts typically present as firm, smooth, mobile nodules, most frequently on the scalp. They are usually asymptomatic but can become inflamed or rupture.

Apply this code when documentation explicitly states a diagnosis of a trichilemmal cyst. This diagnosis is often made clinically, but may be confirmed by excisional biopsy. Supporting documentation should clearly describe the lesion's characteristics and location, consistent with a trichilemmal cyst.

• Differentiate from other epidermal cysts (e.g., epidermal inclusion cyst, sebaceous cyst) which have distinct ICD-10-CM codes.
• Ensure the documentation specifies "trichilemmal" or "pilar" cyst to accurately assign this code.
• If the cyst is inflamed or infected, consider additional codes for associated conditions (e.g., L08.9 for localized infection).