A 45-year-old woman presented with a 3-year history of pulsatile tinnitus in her left ear. She denied hearing loss or otalgia. Past medical history and review of systems were noncontributory. Physical examination revealed a red mass behind the posterior aspect of the tympanic membrane. There was no middle ear effusion, tympanic membrane retraction, or tympanic membrane perforation. External auditory canal was normal in appearance. The patient was subsequently referred for both CT and MRI of the temporal bones and internal auditory canals, respectively, to evaluate for a vascular retrotympanic mass. (Fig.)
Vascular retrotympanic mass
Enhancing retrotympanic mass
Glomus tympanicum
Variant vasculature
Cholesterol granuloma
Tinnitus refers to abnormal ringing in the ears. It may be characterized as pulsatile or continuous and subjective or objective. Subjective tinnitus is perceived by the patient; objective tinnitus may be heard by others during physical examination. In the setting of tinnitus, the physical examination often guides the differential diagnosis and imaging work- up. If a vascular retrotympanic mass is identified on otoscopy, the primary differentials include a glomus tumor, variant vasculature, and cholesterol granuloma. The role of imaging is to exclude variant vasculature prior to biopsy or resection. MRI and CT often play complementary roles.
Glomus tympanicum is a paraganglioma which occurs within the middle ear adjacent to the cochlear promontory. It arises from glomus bodies along the course of Jacobson’s nerve, which is a branch of the glossopharyngeal nerve. The tumor is of neural crest origin and is highly vascular. Clinically, patients present with pulsatile tinnitus, and a vascular retrotympanic mass is visualized on physical examination. Occasionally, patients may experience conductive hearing loss.1
On CT, glomus tympanicum presents as a soft tissue mass along the cochlear promontory with extension into the middle ear space. When large, it may be indistinguishable from other causes of middle ear opacification. The tumor typically does not result in significant ossicular or bony erosion. The MR appearance of glomus tympanicum depends on the size of the lesion. Smaller lesions are hyperintense on T2 sequences with avid enhancement on postcontrast T1 sequences. Larger lesions (greater than 10 mm) may show the characteristic “salt and pepper” appearance secondary to regions of hemorrhage (increased signal intensity) and a combination of flow voids and calcification (decreased signal intensity).2
A high riding internal jugular vein with or without dehiscence is the most common vascular variant affecting the temporal bone. The jugular vein is considered high riding if it extends above the inferior margin of the internal auditory canal. If the sigmoid plate separating the jugular vein from the middle ear cavity is dehiscent, a vascular retrotympanic mass may be seen on physical examination.
An aberrant internal carotid artery is a developmental abnormality which results from agenesis of the cervical and proximal petrous portions of the ICA. As a result, alternate anastamoses form via the external carotid artery. There is collateralization through the inferior tympanic artery (a branch of the ascending pharyngeal artery) to the caroticotympanic branch of the petrous ICA, both of which traverse the middle ear cavity. The enlarged caroticotympanic branch then anastamoses with the horizontal segment of the petrous ICA.3 Cross-sectional imaging demonstrates narrowing and posterolateral deviation of the ICA into the middle ear cavity, along with absence of the cervical and proximal portion of the petrous ICA. Occasionally, a persistent stapedial artery may coexist with an aberrant ICA. Clinically, patients present with pulsatile tinnitus and a vascular retrotympanic mass, similar to a glomus tympanicum.
Cholesterol granuloma occurs secondary to nonspecific chronic inflammatory changes and is most commonly seen in the petrous apex and middle ear cavity. Hemorrhage, cholesterol, and granulation tissue are the hallmarks of the lesion and account for its appearance on MR.4 Patients most often present with conductive hearing loss and a vascular appearing retrotympanic mass on physical examination.
On CT, the imaging appearance is nonspecific with a soft tissue middle ear mass. Findings on MRI are more characteristic, demonstrating a nonenhancing middle ear mass which is hyperintense on both T1 and T2 sequences secondary to hemorrhagic blood products.5 Care must be taken to compare pre and postcontrast T1 sequences, since the lesions are hyperintense on both which may be mistaken for enhancement. With adjacent inflammation, there may be thin peripheral enhancement.
Glomus tympanicum
Cross-sectional imaging is an important component of the work-up and management of patients with tinnitus and a vascular retrotympanic mass. The primary role of imaging is to exclude variant vasculature as the cause of a retrotympanic mass prior to biopsy or resection. MRI and CT play complementary roles. Imaging findings are often characteristic for the clinical differential diagnoses, which include glomus tympanicum, variant vasculature, and cholesterol granuloma. Therefore, knowledge of these imaging patterns is essential when interpreting these studies.
The views expressed in this material are those of the author, and do not reflect the official policy or position of the U.S. Government, the Department of Defense, or the Department of the Air Force.
Betts A, Esquivel C, O'Brien WT Sr. Vascular Retrotympanic Mass. J Am Osteopath Coll Radiol. 2012;1(1):31-33.
Dr. Betts and Dr. O'Brien work with the Department of Diagnostic Imaging, Wilford Hall Ambulatory Surgical Center, San Antonio, TX and Dr. Esquivel works with the Department of Otolaryngology, Wilford Hall Ambulatory Surgical Center, San Antonio, TX .
