Giant epidermal inclusion cyst of the axilla: a case report with diagnostic ultrasound imaging features

Epidermal inclusion cyst is a relatively common benign lesion of the skin, and it can occur anywhere in the hair-bearing area of the body. It usually appears as an asymptomatic mass, which is less than 4 cm in size. However, rarely it can occur as a large mass in the axilla, and in such cases, the location and size tend to cause more complications. The author encountered a patient with a large epidermal inclusion cyst of the axilla. Ultrasound examination showed an oval-shaped hypoechoic subcutaneous mass with dermal attachment, intralesional echogenic reflectors, filiform anechoic areas, and no vascularity. These characteristic imaging features could lead to an accurate preoperative imaging diagnosis without biopsy and avoid subsequent complications. Excision of the mass was performed due to discomfort because of the large size and growing nature of the lesion, and histological examination confirmed the diagnosis of an epidermal inclusion cyst. Therefore, recognition of diagnostic ultrasound features of this entity may enable an accurate preoperative diagnosis, even when it has an unusual size and location.