A Transient, Postauricular Arteriovenous Fistula Masquerading as Acute Mastoiditis

Background Vascular lesions of the skull base are diverse in terms of etiology and natural history. Outside of neoplasm, most entities in this category represent congenital or acquired malformations of arteries, veins, or both. In some cases, such as that of a posttraumatic, direct cavernous carotid fistula, symptoms are quickly apparent and rapidly progressive after formation. In other cases, symptoms and clinical findings can be relatively occult for years. We present a case of a postauricular arteriovenous fistula (AVF) that initially masquerated as a subperiosteal abscess only to self-resolve.

Case Presentation A 47-year-old woman liver transplant recipient with history of hepatitis C, alcohol abuse, diabetes mellitus type II, and maxillofacial trauma during a motor vehicle accident 16 years prior presented to the otolaryngology service of a tertiary referral hospital with right postauricular swelling. She was initially admitted to the hospital for acute renal failure. Due to the additional finding of right postauricular swelling along with complaints of right-sided headaches, an otolaryngology consult was sought for a possible diagnosis of acute mastoiditis. On exam, ∼2 cm by 1 cm, fluctuant and easily compressible mass were found to involve the right postauricular skin. There was no erythema or edema of the surrounding skin, and the lesion in question was found to be blue in hue and pulsatile. Imaging was sought to further characterize this lesion. Due to the patient’s acute kidney injury, it was felt that contrast agents should be avoided in her diagnostic evaluation. On the suspicion that this mass represented a vascular lesion, an MRA of the head and neck without contrast was also obtained, which correlated the postauricular and occipital lesions with AVF of the scalp. No intervention was sought initially. Months after the initially presentation, the patient presented for re-evaluation in an outpatient setting and was found to have no evidence of the previously seen lesion. Doppler ultrasound of the postauricular skin where the lesion had previously been seen was performed, and no vascular flow was identified.

Conclusion AVFs of the scalp, previously termed cirsoid aneurysms, occur when an abnormal connections between arterial vessels and draining veins form without a capillary bed, leading to venous dilation. As is seen in the present case, the AVF may present several years after trauma. This case represents a rare occasion in which an AVF can self-resolve without intervention.