FLEX January 2024

Clinical Review & Education Review

Diagnostic Approach to Pulsatile Tinnitus

panic paragangliomas derive from parasympathetic paraganglia in association with the auricular branch of the vagus nerve or the tym panic branch of the glossopharyngeal nerve, and manifest on imaging as avidly-enhancing hypervascular masses arising from the coch lear promontory or in the jugular foramen, sometimes with con comitant permeative-destructive changes in the bone ( Figure1 ).Mar ginal sinus dAVF is sometimes confused for a jugular paraganglioma on MRI, and catheter angiography may be needed to differentiate these. Patients with jugulotypanic paragangliomas almost always have PT, but later in their course can also present with cranial nerve palsies or conductive hearing loss owing to impingement on the os sicular chain. Their PT typically does not change with jugular vein compression or occipital artery compression, but can be exacer bated by exercise. Symptoms are insensitive to position (lying/ standing) or the Valsalva maneuver. On otoscopic examination, a ret rotympanic vascular mass is often seen. Depending on the stage of the disease, treatment can involve resection, embolization, exter nal beam radiation, or systemic radionuclide therapy. Vestibular schwannomas are benign tumors of the Schwann cells that arise from the vestibular portion of the eighth cranial nerve. Patients with schwannomas most commonly present with asymmetrical sensorineural hearing loss. More than 60% of patients with vestibular schwannoma have tinnitus. 12 Sensorineu ral hearing loss ipsilateral to PT symptoms should raise concern for schwannoma. Otoscopic examination is normal. Vestibular testing frequently reveals decreased ipsilateral function; this can be seen on bedside examinations with the head impulse test. On MRI findings, vestibular schwannomas are enhancing cylindrical or conical masses in the internal auditory canal, cerebellopontine angle, or cochlea. Cysts in the tumor can be seen as well. Treat ment strategies involve observation, microsurgery, or stereotactic radiation. Intracochlear schwannomas are less common but are often missed—these manifest as a small focus of enhancement in the inner ear on T1-weighted, fat-saturated, postcontrast sequences, and sometimes as a small mass on high spatial resolu tion 3D balanced steady state gradient echo sequences (eg, FIESTA or TrueFISP; Figure2 ). When counseling patients with PT likely owing to an intracochlear schwannoma, it is important to inform them that they will lose hearing if the tumor is resected. Intracochlear schwannomas are typically slow growing and may be best managed with continued observation. Hearing aids or implantable devices are often needed for hearing rehabilitation. Thinning or absence of the superior aspect of the bone overly ing the superior semicircular canal can result in alterations of the mi crofluid mechanics of the hearing apparatus, resulting in increased audibility of any internal sound, including brain pulsations. 13 Vary ing symptoms including vertigo, aural pressure, conductive hear ing loss, or autophony can result. Loud sound can induce vertigo in this condition, known as Tullio phenomenon. Although the diagno sis can be suggested by balanced steady-state free precession (eg, FIESTA) MRI, temporal bone CT, and VEMP (vestibular evoked myo genic potential) testing can help establish the diagnosis of semicir cular canal dehiscence (SSCD). Surgical repair is generally of ben efit. The cause of SSCD is unknown. Dehiscences of the tegmen tympani ( Video ) or tegmen mastoidium can also cause PT, and may be related to prior surgery or chronic otitis media. Dehiscence of the cortical plate overlying the sigmoid sinus may amplify venous sound perception in patients and cause PT. 14 Sigmoid sinus cortical plate

neoplasms, and Meniere disease. Superior canal dehiscence can pro duce a unique pattern on audiometry, with suprathreshold low frequency bone conduction, decreased air conduction thresholds, and normal acoustic reflexes. Transcanal sound recordings can also be performed to objectively record PT. After recording the sounds using a transcanal microphone, the magnitudes of the frequencies are converted to dB sound pressure levels in time- and time frequency domains using short-time Fourier transformation. 8 Imaging We use magnetic resonance imaging (MRI) as the first-line diagnos tic imaging modality for PT evaluation. Overall, MRI has the highest sensitivity for detecting the most dangerous potential causes of PT (dAVF, arterial disease, intracranial hypertension, and neoplasms), and does not expose the patient to ionizing radiation. In addition to diffusion-weighted, T2-weighted FLAIR, and pre- and post-3D T1 weighted sequences, we obtain time-of-flight magnetic resonance angiogram (MRA), pseudocontinuous arterial spin labeling (ASL), and time-resolved MRA sequences to assess the vasculature (eTable 2 in the Supplement). 9 For patients with hearing loss and no cause of PT identified on MRI, high-resolution temporal bone computed to mography (CT) can be helpful to assess for superior canal dehis cence, sigmoid wall abnormalities, and other structural abnormali ties of the hearing apparatus. Patients who cannot obtain MRI due to metallic implants, claustrophobia, or cost sometimes undergo computed tomographic angiogram as an alternative, despite this mo dality’s lower sensitivity for idiopathic intracranial hypertension (IIH) and dAVF. Diagnostic cerebral angiograms are performed if an ar terial cause of PT or dAVF is suspected based on medical history, physical examination, or imaging. Image-guided lumbar puncture (LP) with recording of opening pressure is performed if IIH is sus pected. In addition, in patients with suspected venous PT, we as sess patients’ degree of symptoms before and after removal of 20 mL of cerebrospinal fluid (CSF) via LP by asking them their subjec tive PT rating from 1 to 10 and by obtaining magnetic resonance venograms. 10 We also measure the closing pressure after the CSF is drained. This process allows us to determine if the symptoms are from a venous stenosis that will improve by lowering CSF pressure, which can often be achieved with conservative treatment of IIH (ie, acetazolamide and weight loss). If the patient has a venous steno sis, and the symptoms are owing to the stenosis, but the PT is not improved with lowering the ICP via CSF removal, the patient may have a “fixed stenosis” —one that is recalcitrant to lowering the ICP. These patients’ symptoms may not improve with conservative treatment.

Discussion: Diagnosis by Category Structural Causes of PT

Structural causes of PT are detectable on MRI or CT of the head and neck, and include neoplasms and temporal bone pathologic abnor mality. The most common neoplasms causing PT are paraganglio mas and schwannomas. Paragangliomas are neuroendocrine tumors derived from the embryonic neural crest, and most of those found in the skull base and neck have been linked to pathogenic variants in genes encod ing the succinate dehydrogenase enzyme complex. 11 Jugulotym

478 JAMA Otolaryngology–Head & Neck Surgery May 2022 Volume 148, Number 5 (Reprinted)

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