A 61-year-old male patient presented to the clinic with a history of recurrent upper respiratory infections, chronic ear fullness, and right-sided otalgia. An outside otolaryngologist had recommended pressure equalizer (PE) tubes, which were placed three years ago. Once his tube came out, the fullness in the ear returned, necessitating replacement a year later. When he had the tube in place, he had drainage from his ear intermittently. In addition, he reported headaches, blurry vision, and pulsing right eye pain. He has no history of previous ear issues as a child or adult. Physical examination demonstrates a serous middle ear effusion (Fig. 1). The left side was normal. Audiogram demonstrated mixed mild to moderately severe hearing loss on the right and mild high-frequency sensorineural hearing loss on the left.Figure 1: Otoscopic image of the patient’s right ear. Audiology, serous middle ear effusion.Figure 2: Axial (horizontal) T1 pre-contrast MRI of the brain demonstrating a hyperintense (bright) mass of the right petrous apex that is brighter than the surrounding brain and anterior to the right IAC. Audiology, serous middle ear effusion.Figure 3: Axial (horizontal) T2-weighted MRI image demonstrating that the mass remains bright on T2. Audiology, serous middle ear effusion.Figure 4: Axial (horizontal) CT image showing the right petrous apex mass with erosion of the right eustachian tube. Note the normal appearance of the left eustachian tube. Audiology, serous middle ear effusion.Figure 5: Axial (horizontal) CT image demonstrating the right petrous apex mass with erosion of the bony carotid canal. Note the normal appearance of the left carotid canal. Audiology, serous middle ear effusion.Table 1: Petrous Apex Lesions.DIAGNOSIS: PETROUS APEX CHOLESTEROL GRANULOMA Unilateral serous middle ear effusion, especially in adults, requires further investigation and workup. Though unilateral serous middle ear effusion can be caused by Eustachian tube function, the patient had no history of Eustachian tube function prior to three years ago. The first step in workup of unilateral serous effusion is to perform nasopharyngoscopy to evaluate for a nasopharyngeal mass occluding the Eustachian tube. Nasopharyngeal masses can range from benign sinonasal polyps or tumors to malignancies such as nasopharyngeal carcinoma or clival chordoma. If no mass is identified, and the patient has no history of Eustachian tube dysfunction, recent upper respiratory infection, or allergic rhinitis/significant reflux, an MRI or CT scan should be obtained for further evaluation. Lastly, if this is nondiagnostic, blood tests such as ANCA should be obtained to evaluate for an underlying autoimmune etiology, including granulomatosis with polyangiitis (aka Wegener’s granulomatosis), which can cause inflammatory serous otitis media. In our patient, a petrous apex lesion was discovered on MRI, which was occluding the right sided eustachian tube, causing a unilateral serous middle ear effusion (Figs. 2, 3). The petrous apex is the most medial part of the temporal bone and is divided into anterior and posterior aspects by the internal auditory canal. It poses a surgical challenge due to its medial location and proximity to the cochlea, carotid artery, jugular vein, labyrinth, brain, and facial and other cranial nerves. Pathologies involving the petrous apex include a wide differential diagnosis, i.e., petrous apex effusion, cholesterol granuloma, cholesteatoma, mucocele, and benign and malignant tumors (Table 1). Our patient was found to have a petrous apex cholesterol granuloma on MRI, the most common mass identified in the petrous apex. Cholesterol granulomas can be distinguished from other petrous apex pathology on imaging, as they are hyperintense (brighter than the brain) on both T1- and T2-weighted MRI and do not enhance with contrast. Additionally, they are hyperintense in fluid-attenuated inversion recovery MRI but have low intensity (dark) on diffusion-weighted imaging. CT imaging of the temporal bones is also useful for surgical planning and preoperative evaluation of involved structures. CT will typically demonstrate expansile erosive changes of the involved side with a contralateral -normal-appearing aerated petrous apex. On MRI, this patient’s lesion appeared hyperintense on both T1 and T2, and serial imaging demonstrated growth of the granuloma laterally, anterior to the cochlea (Figs. 2 and 3). CT scan showed extension of the mass into the Eustachian tube and the bony carotid canal (Figs. 4, 5). Cholesterol granulomas are cysts in the temporal bone that are hypothesized to arise from bleeding within a mucosal-lined cavity. This may be caused by expansion of air-filled spaces infiltrating into adjacent bone marrow, causing build-up of negative pressure, followed by hemorrhage and subsequent granulation tissue formation. 1 However, they are not true cysts, as they lack an epithelial lining. Cholesterol granulomas are rare; they are estimated to occur in 0.6 persons per 1 million. The most common symptom associated with cholesterol granulomas is hearing loss, followed by vestibular symptoms, tinnitus, and headache. 1 Treatment of cholesterol granulomas depends on size, growth, and the amount of symptoms the patient is having. If small, stable in size, and asymptomatic, cholesterol granulomas can be observed with serial imaging. We prefer the use of non-contrast internal auditory canal MRI to reduce radiation exposure. However, cholesterol granulomas that are enlarging or involving critical structures must be managed to prevent further destruction into the carotid canal, jugular bulb, Eustachian tube, cochlea, or labyrinth. Surgical management of cholesterol granulomas is aimed at creating a drainage pathway so the granuloma does not continue to expand into surrounding structures. These lesions do not generally need to be fully excised because they lack an epithelial lining. Depending on the location, this can be accomplished via infracochlear, transmastoid, or middle fossa approaches. Additionally, medial lesions can be accessed endoscopically via a transsphenoidal and/or transpterygoid approach. However, the infracochlear approach remains the most common and has the benefit of preserving hearing as well as being a less invasive, transcanal surgery that spares the patient from craniotomy. The infracochlear approach involves drilling under the cochlea between the carotid artery and jugular vein. 2–4 In this method, the superior limit of the dissection is the round window, the anterior limit is the carotid artery, and the posterior limit is the jugular vein. Endoscopes are often used as an adjunct for improved visualization. The surgeon can then reach the inferior aspect of the lesion to drain it into the middle ear. Once entered, the hallmark of cholesterol granuloma is the dark brown “motor oil” fluid that drains from it. Drainage is often accompanied by stent placement (with silastic [silicone] or other material) to prevent the lesion from reforming. If the thick cystic fluid overwhelms the middle ear, it may require placement of a PE tube to drain the fluid into the outer ear. However, normally this fluid will continue to drain through the Eustachian tube. These patients then need to be monitored with intermittent MRI imaging to ensure that the lesion is decreasing in size and does not recur. Our assessment is petrous apex cholesterol granuloma demonstrated enlargement between 2018 and 2020. The patient ultimately underwent right transtympanic approach to drain the cholesterol granuloma. In this patient, the cholesterol granuloma had pushed and obstructed the Eustachian tube and was protruding into the middle ear. This allowed exposure and drainage of the cholesterol granuloma into the middle ear with placement of a silastic stent. He is now doing well with overall improvement of his symptoms and resolution of his symptoms. BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS Watch the patient videos online at thehearingjournal.com. Read this month’s Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient’s imaging for yourself. Video 1. Axial (horizontal) CT of the temporal bones showing the anatomical relationship between the lesion and the inner ear structures and the IAC. Video 2. Coronal (vertical parallel to the face) CT of the temporal bones showing the coronal anatomy of the petrous apex lesion. Video 3. Sagittal CT of the temporal bones (from the right side) demonstrating the anatomy of the corridor used to drill an opening to drain the cyst using an infracochlear approach. Video 4. Axial (horizontal) T1-weighted images of the brain performed in 2021 showing hyperintesity (bright) petrous apex mass on the right. Video 5. Axial (horizontal) T2-weighted images of the brain from 2021 demonstrating the hyperintense (bright) petrous apex mass on the right. Video 6. Axial (horizontal) T2 weighted images from 2018 study showing the smaller cyst at that time.