Neurologic Imaging

What Is the Best Initial Imaging for Pulsatile Tinnitus with a Retrotympanic Lesion?

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What Is the Best Initial Imaging for Pulsatile Tinnitus with a Retrotympanic Lesion?

A 48-year-old patient presents to your clinic describing a rhythmic “whooshing” sound in her left ear, perfectly in sync with her heartbeat. The sound is distracting and has been present for several months. On otoscopy, you identify a reddish, pulsatile mass behind an intact tympanic membrane. This classic presentation of unilateral pulsatile tinnitus with a visible retrotympanic lesion points toward a specific set of middle ear pathologies. The immediate clinical question is which imaging study to order first to confirm the diagnosis and guide management. According to the American College of Radiology (ACR) Appropriateness Criteria, the initial imaging study for this scenario is clear: `CT temporal bone without IV contrast` is rated Usually appropriate.

Who Fits This Clinical Scenario?

This diagnostic workflow is specifically for patients presenting with two key findings: pulsatile tinnitus and a suspected retrotympanic lesion on otoscopy. The tinnitus can be unilateral or bilateral, but it must be pulsatile—a rhythmic sound that corresponds to the patient’s pulse. The otoscopic finding is crucial; the clinician must visualize an abnormality behind the tympanic membrane, such as a blue or red mass, which may or may not be visibly pulsating.

This guidance does not apply to patients with similar but distinct presentations. It is critical to differentiate this scenario from:

  • Pulsatile tinnitus with a normal otoscopic exam: This presentation suggests a different underlying cause, often a vascular anomaly outside the middle ear like a dural arteriovenous fistula or carotid stenosis. That patient follows a separate ACR imaging pathway, typically starting with CTA or MRA.
  • Nonpulsatile tinnitus: Patients who describe a constant ringing, buzzing, or hissing sound without a pulse-synchronous character fall into a different category. Their workup is guided by factors like laterality, hearing loss, and neurologic deficits.

Applying this article’s workflow to a patient without a visible retrotympanic lesion can lead to a missed diagnosis, as the recommended study here is optimized for middle ear anatomy, not for screening the entire head and neck vasculature.

What Diagnoses Are You Working Up in This Scenario?

When a pulsatile mass is seen behind the eardrum, the differential diagnosis is narrow and centered on specific vascular structures and tumors within the middle ear cavity. The primary goal of initial imaging is to differentiate among these possibilities, as their management differs significantly.

The most common cause is a glomus tympanicum paraganglioma. These are benign, highly vascular neuroendocrine tumors that arise from glomus bodies along Jacobson’s nerve on the cochlear promontory. They classically appear as a reddish pulsatile mass behind the tympanic membrane and are the most frequent tumor of the middle ear.

Another key consideration is an aberrant internal carotid artery (ICA). In this congenital anomaly, the vertical segment of the petrous ICA is absent, and blood flow is rerouted through an enlarged inferior tympanic artery, which then enters the middle ear cavity before rejoining the horizontal petrous segment. This creates a pulsatile vessel directly within the middle ear space, which can be mistaken for a tumor and is at high risk of catastrophic injury during middle ear surgery.

A dehiscent or high-riding jugular bulb is also on the differential. This occurs when the bony plate (sigmoid plate) separating the jugular bulb from the middle ear is absent, allowing the bulb to protrude into the middle ear cavity. This can present as a blue, compressible mass and is another critical finding to identify before any potential middle ear procedure.

Less common possibilities include cholesterol granulomas, middle ear adenomas, or hemangiomas, though the classic pulsatile nature strongly points toward a vascular or highly vascularized lesion.

Why Is CT Temporal Bone Without IV Contrast the Recommended Study?

For a patient with pulsatile tinnitus and a visible retrotympanic mass, the ACR designates `CT temporal bone without IV contrast` as Usually appropriate. The rationale is grounded in the test’s exceptional ability to visualize the fine bony anatomy of the temporal bone, which is the key to differentiating the primary diagnostic considerations.

This non-contrast study provides exquisite detail of the osseous structures that define the middle ear. It can clearly identify the smooth-bordered soft tissue mass of a glomus tympanicum localized to the cochlear promontory. Critically, it can also reveal the bony erosion characteristic of a more aggressive glomus tumor. For an aberrant ICA, CT will demonstrate the absence of the normal carotid canal and the presence of a vessel coursing through the middle ear. For a dehiscent jugular bulb, it will show the absence of the sigmoid plate covering the bulb. Because these primary diagnoses are defined by their relationship to bone, a non-contrast CT is often sufficient for a definitive diagnosis.

Why are other studies rated lower for this initial workup?

  • CTA Head and Neck with IV Contrast: While rated May be appropriate, it is not the preferred first step. It adds IV contrast and a higher radiation dose (adult RRL ☢☢☢ 1-10 mSv) to answer a question that can often be solved without contrast. While CTA is excellent for defining the vascular supply, this is typically a secondary question addressed after the initial diagnosis is made, especially if a paraganglioma is found and presurgical embolization is considered.
  • MRI/MRA of the Head: These studies are rated Usually not appropriate for the initial evaluation in this specific scenario. MRI offers poor visualization of the fine bony anatomy of the temporal bone, making it difficult to diagnose a dehiscent jugular bulb or delineate the precise course of an aberrant carotid artery. While MRI is excellent for soft tissue characterization and will be used downstream, it is not the optimal first test to answer the primary anatomical question.

The recommended non-contrast CT of the temporal bone carries a relative radiation level of ☢☢☢ (1-10 mSv). This moderate dose is justified because it directly and efficiently answers the clinical question, preventing diagnostic delays and the need for more complex, higher-dose studies upfront.

What’s Next After CT Temporal Bone? Downstream Workflow

The results of the initial non-contrast CT of the temporal bone will dictate the subsequent clinical and imaging pathway. The workflow branches based on whether the findings are positive, negative, or indeterminate.

If the CT is positive for a suspected glomus tympanicum: The diagnosis is largely established. The next step is typically further characterization and staging. An MRI/MRA of the head and neck with IV contrast is often ordered to assess the full extent of the tumor, look for intracranial extension, and screen for multicentric paragangliomas (e.g., glomus jugulare, carotid body tumors), which occur in a meaningful number of cases. This advanced imaging also helps in treatment planning, whether it involves surgery, radiation, or observation.

If the CT confirms an aberrant ICA or dehiscent jugular bulb: The diagnosis is made, and the primary role of imaging is complete. Management for these congenital vascular variants is typically conservative unless they are causing significant conductive hearing loss or other complications. The key is now awareness; this finding must be clearly documented in the patient’s record to prevent iatrogenic injury during any future otologic procedures.

If the CT is negative or indeterminate: This is an uncommon outcome given the positive otoscopic finding. If the CT shows no clear bony erosion or vascular anomaly but a soft tissue density persists, the clinician should reconsider the differential. An MRI of the head and internal auditory canal with IV contrast may be the next logical step to better characterize the soft tissue lesion, which could be a less common entity like a middle ear adenoma or schwannoma. Close collaboration between the otolaryngologist and radiologist is essential in these cases.

Pitfalls to Avoid (and When to Get Help)

Navigating this specific clinical scenario requires precision to avoid common diagnostic errors. Here are several pitfalls to watch for:

  • Ordering the wrong CT: A “CT Head” is not the same as a “CT Temporal Bone.” The latter uses high-resolution, thin-slice acquisition protocols optimized for the tiny structures of the middle and inner ear. Ordering a routine head CT will likely miss the diagnosis.
  • Misinterpreting the clinical scenario: Do not apply this workflow to a patient with pulsatile tinnitus but a normal otoscopy. That patient needs a vascular workup (CTA/MRA) first, as the cause is likely outside the middle ear.
    • Assuming a solitary lesion: If a paraganglioma is found, remember the potential for multicentricity. The workup is not complete until the rest of the head and neck have been appropriately screened for other paragangliomas, usually with contrast-enhanced MRI or CTA.
  • Inadequate clinical history: Failing to inform the radiologist of the specific finding of a “pulsatile retrotympanic mass” on the imaging requisition can lead to a non-specific read. Providing this key clinical context focuses the radiologist’s search.

If the imaging findings are complex or do not align with the clinical picture, escalation to a head and neck radiologist or a multidisciplinary skull base conference is the appropriate next step.

Related ACR Topics and Tools

For a comprehensive overview of imaging for all types of tinnitus, including scenarios without a visible lesion, please consult our parent guide. For tools to help with ordering, protocoling, and patient communication, see the resources below.

Frequently Asked Questions

Why is a non-contrast CT recommended first instead of a CTA or MRA?

A non-contrast CT of the temporal bone is recommended first because it provides the best visualization of the fine bony anatomy of the middle ear. The most common causes for a pulsatile retrotympanic mass, such as a glomus tympanicum, aberrant carotid artery, or dehiscent jugular bulb, are primarily diagnosed by their characteristic relationship to these bony structures. This often makes contrast unnecessary for the initial diagnosis, avoiding its associated risks and costs.

What if the otoscopic exam is uncertain? Should I still order the CT temporal bone?

If you are uncertain about the presence of a retrotympanic lesion, the optimal imaging pathway is less clear. The workup for pulsatile tinnitus with a normal otoscopy is different and focuses on vascular imaging like CTA or MRA. If your suspicion for a middle ear lesion is low, it may be more appropriate to follow the ‘normal otoscopy’ ACR variant or refer to an otolaryngologist for a definitive microscopic examination before ordering imaging.

Is there a role for ultrasound in this scenario?

No. According to the ACR Appropriateness Criteria, carotid duplex ultrasound and transcranial Doppler ultrasound are rated ‘Usually not appropriate’ for this specific clinical scenario. These modalities cannot visualize the structures within the middle ear and temporal bone and therefore have no role in evaluating a suspected retrotympanic lesion.

If the CT shows a glomus tympanicum, is MRI always necessary?

Yes, in most cases, an MRI/MRA of the head and neck with contrast is the recommended next step after a CT diagnosis of a glomus tympanicum. The MRI helps determine the full extent of the tumor, assesses for any intracranial involvement, and is crucial for screening for additional, synchronous paragangliomas elsewhere in the head and neck, which can significantly alter the management plan.

Can I order a CT temporal bone ‘with and without contrast’ from the start to save time?

While technically possible, the ACR guidelines rate ‘CT temporal bone without and with IV contrast’ as ‘Usually not appropriate’ for the initial workup. Starting with a non-contrast study is more efficient and adheres to the ALARA (As Low As Reasonably Achievable) principle for radiation safety. The contrast portion is often unnecessary if a clear diagnosis of a vascular variant like an aberrant carotid is made on the non-contrast images. It is better to perform imaging in a stepwise fashion based on the initial findings.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026