Superficial Temporal Artery Pseudoaneurysm Presenting as A Suspected Sebaceous Cyst

Abstract

A 20-year-old man presented to the emergency department (ED) requesting to have a “cyst” on his scalp drained. The patient stated that he had first noticed the cyst about 1.5 years ago, which seemed to develop after he was hit on the head during an altercation. He reported that it was drained in this ED 6 to 8 months earlier but that it did not resolve. On examination, the left temporal scalp had a 2-cm indurated cystic subcutaneous lesion that was minimally tender, without any drainage or overlying erythema. The patient was advised that it appeared to be sebaceous cyst, which would likely recur until formally excised. Because of his mild discomfort, he opted for incision and drainage pending his clinic referral. After alcohol preparation and local anesthesia, the incision yielded only brisk bleeding that was easily controlled with fingertip pressure but required suture placement for complete hemostasis. The lesion was felt to be faintly pulsatile while holding pressure. Point of care (POC) ultrasound evaluation performed with a high frequency linear array probe revealed the cyst (Figure 1) to be a superficial temporal artery (STA) pseudoaneurysm. Standard B mode imaging clearly showed turbulent blood flow (Video 1). Color Doppler ultrasound imaging (Video 2) showed the typical swirling of blood within the aneurysm (the “yin-yang” sign). Vascular surgery was consulted and arrangements were made for outpatient excision of the lesion. At surgery approximately 1 month later, the lesion was confirmed to be a pseudoaneurysm.