Imaging of pulsatile tinnitus: basic examination versus comprehensive examination package.

Tinnitus is a common clinical syndrome with rare radiologic findings . This human malady may exist in two forms, namely objective or subjective. Objective tinnitus is a real sound produced outside the inner ear, which is heard by the patient and also by the examining physician. Subjective tinnitus is heard only by the patient and involves the neural mechanisms of the ear or auditory pathways. These pathways extend from the tectorial membrane and hair cells of the inner ear through the organ of Corti, cochlear nerve, cochlear nucleus, brain stem, midbrain, and auditory cortex. In some patients, the tinnitus is described as pulsatile, a sound that is synchronous with the cardiac pulsations. Pulsatile tinnitus is often subclassified as objective (which the examining physician can hear) or subjective (which only the patient can hear). The neurootologic work-up of patients with tinnitus includes complete clinical evaluation including tympanometric, audiometric, and auditory evoked potential investigations. A specific tinnitus evaluation is also performed to match the pitch and intensity of the sounds, which helps to indicate the likely source. The clinical evaluation may demonstrate a mechanical type of tinnitus (muscle myoclonus) or a plug of cerumen or hair in the external auditory canal. Such patients require few tests and are often treated by section of the tendon of the offending muscle or removal of the debris from the external auditory canal. If the problem is not solved by clinical examination or neurootologic tests, the patient is then referred for radiologic evaluation (1). In this issue of the American Journal of Neuroradio/ogy, Dietz et al describe the use of magnetic resonance (MR) and MR angiography (MRA) in the evaluation of patients with pulsatile tinnitus (2). The authors show that MR and MRA may serve as substitutes for computed tomography (CT) and conventional angiography in patients with objective pulsatile tinnitus. Evaluation of patients with subjective pulsatile tinnitus remains problematic. The authors studied 49 patients, 28 of whom had positive radiologic findings . Of these 28 patients, 16 had objective pulsatile tinnitus and 12 patients had subjective pulsatile tinnitus. In the 28 positive studies, 10 cases had CT and 17 cases had conventional angiography. The remaining 21 patients with normal MR/ MRA findings all had subjective pulsatile tinnitus and a normal clinical examination. Of these 21 patients, only 1 patient had conventional angiography and none had a CT scan. The authors do not discuss the need for high-resolution temporal bone CT or conventional angiography in patients with normal MR/ MRA studies. Thus, the value of a normal MR/ MRA examination is not known. A portion of the article describes the value of MRA in the work-up of patients with dural fistulas (extracranial shunts) and/or arteriovenous malformations (A V Ms) (both intracranial and extracranial shunts). The subpial variety of AVMs is quite common. A less common type of A V M is the dural variety, which derives its blood supply primarily from the external carotid artery with venous drainage outside or inside the brain. The direction of venous drainage is the determinant of the clinical symptoms. The presenting symptoms may include pulsatile tinnitus and/ or an audible bruit in patients with extracranial drainage of subpial A V Ms or dural fistulas (3). Conventional MR may not detect dural fistulas or purely dural A V Ms, unless the venous drainage extends into the intracranial cavity or into the scalp (4). As clearly shown by the authors, the addition of an MRA examination is invaluable. Another valuable point in the article describes the use of MRA in