Neurologic Imaging

What Imaging Should You Order for New-Onset Anosmia? An ACR-Guided Workflow

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What Imaging Should You Order for New-Onset Anosmia? An ACR-Guided Workflow

A 58-year-old patient presents to your clinic with a six-month history of progressively worsening loss of smell. It started subtly, but now they can’t detect the scent of coffee brewing or notice if food is burning. There was no preceding viral illness, head trauma, or known allergies. The physical exam, including a basic nasal inspection, is unrevealing. You suspect a process affecting the olfactory nerve (CN I) and need to decide on the most appropriate initial imaging study to investigate the cause. This article provides a detailed clinical workflow for this exact scenario, grounded in the American College of Radiology (ACR) Appropriateness Criteria. For a patient with new-onset anosmia, the ACR designates MRI of the orbits, face, and neck without and with IV contrast as Usually Appropriate.

Who Fits This Clinical Scenario for Anosmia Imaging?

This guidance applies to adult patients presenting with new, persistent, or progressive abnormalities of the sense of smell—including anosmia (complete loss), hyposmia (reduced sense), or parosmia (distorted sense)—where a clear, self-limited cause like a common cold or acute sinusitis has been ruled out. The key factor is that the olfactory deficit is the primary, isolated neurologic finding at the time of presentation.

This workflow is specifically for the initial imaging workup when the cause is unknown. It is less applicable if a clear diagnosis, such as extensive nasal polyposis, is already evident on nasal endoscopy.

Crucially, this guidance should be distinguished from scenarios involving other cranial nerves. This workflow is NOT intended for patients who also present with:

  • Unilateral facial weakness or hemifacial spasm, which suggests a pathology of the facial nerve (CN VII).
  • Weakness of the mastication muscles or trigeminal sensory loss, pointing to a trigeminal nerve (CN V) issue.
  • Vocal cord paralysis or dysphagia, which would direct the workup toward the vagus (CN X) or glossopharyngeal (CN IX) nerves.

If multiple cranial neuropathies are present, a different diagnostic algorithm is required to investigate lesions at the skull base or within the brainstem.

What Diagnoses Are You Working Up With Imaging for Anosmia?

When ordering imaging for isolated anosmia, the goal is to investigate the entire olfactory pathway, from the nasal mucosa to the olfactory cortex. The differential diagnosis spans benign inflammatory conditions to critical intracranial pathologies.

A primary concern is an anterior cranial fossa mass. An olfactory groove meningioma is a classic, slow-growing benign tumor that can compress the olfactory bulbs and tracts, often presenting with anosmia long before other neurologic symptoms appear. Similarly, an esthesioneuroblastoma (olfactory neuroblastoma), a rare malignant tumor arising from the olfactory epithelium, is a critical diagnosis not to miss. These masses are often invisible on routine physical examination.

Extensive sinonasal inflammatory disease is a common cause of olfactory dysfunction. While some conditions like chronic rhinosinusitis or nasal polyposis can be suspected clinically, imaging is definitive. It can reveal the extent of mucosal thickening, sinus opacification, and any bony erosion that might suggest a more aggressive process.

Less commonly, granulomatous or inflammatory conditions can infiltrate the sinonasal region and skull base. Sarcoidosis or granulomatosis with polyangiitis can present with sinonasal symptoms, including anosmia, and imaging helps identify the characteristic soft tissue involvement that would prompt a biopsy.

Finally, while neurodegenerative diseases like Parkinson’s disease and Alzheimer’s disease are strongly associated with olfactory loss, imaging in these cases is primarily to exclude the structural causes listed above. The findings related to neurodegeneration itself (e.g., cortical atrophy) are typically nonspecific in the early stages.

Why Is MRI of the Orbits, Face, and Neck the Recommended Study for Anosmia?

The ACR rates MRI of the orbits, face, and neck without and with IV contrast as “Usually Appropriate” because it provides the most comprehensive evaluation of the complex anatomy involved in olfaction. This specific protocol is superior to a routine brain MRI for several key reasons.

First, MRI offers unparalleled soft-tissue contrast, which is essential for visualizing the small olfactory bulbs and tracts as they sit in the cribriform plate. High-resolution, thin-slice sequences can detect subtle atrophy or abnormal enhancement of these structures. Second, the inclusion of intravenous contrast is critical for identifying and characterizing potential masses like meningiomas or esthesioneuroblastomas, which typically enhance avidly. Contrast also highlights areas of inflammation in the sinonasal mucosa or dura.

The wide field of view—encompassing the orbits, face, and neck—is intentional. It allows for a complete assessment from the nasal cavity, through the paranasal sinuses, up to the anterior cranial fossa, and includes the adjacent structures where pathology could extend. This single study effectively evaluates for sinonasal, intracranial, and skull base pathology simultaneously.

Alternative studies are rated lower for this initial workup:

  • CT of the maxillofacial region without IV contrast is rated “May be appropriate.” While excellent for evaluating bony anatomy and sinus opacification, it provides very limited detail of the olfactory bulbs, tracts, and other intracranial soft tissues. It is a reasonable choice if the pre-test probability for simple chronic rhinosinusitis is very high, but it is an incomplete neurologic workup. This study involves a low dose of ionizing radiation (adult RRL=☢☢ 0.1-1mSv).
  • MRI of the head without and with IV contrast is rated “May be appropriate (Disagreement).” A standard brain MRI protocol may not include the dedicated thin-slice coronal sequences through the anterior cranial fossa necessary to properly evaluate the olfactory apparatus. This can lead to a false-negative study. Ordering the specific “orbits, face, and neck” protocol ensures the radiologist uses the correct sequences to answer the clinical question.

What’s Next After MRI? Downstream Clinical Workflow

The results of the MRI will guide your next steps, branching into distinct clinical pathways.

If the study is positive for a mass lesion (e.g., suspected meningioma or esthesioneuroblastoma), the immediate next step is a referral to Neurosurgery and often Otolaryngology (ENT) for a multidisciplinary evaluation. Further management will likely involve surgical planning, possibly with additional imaging like a CT to better delineate bony involvement, and biopsy for definitive tissue diagnosis.

If the study is positive for extensive sinonasal inflammatory disease (e.g., chronic rhinosinusitis with polyposis), the patient should be referred to an Otolaryngologist. The downstream workflow will focus on medical management (e.g., nasal steroids, biologics) and potential surgical intervention (e.g., functional endoscopic sinus surgery) to improve nasal airflow and reduce inflammation.

If the study is negative and reveals no structural abnormality, the diagnosis is often idiopathic or post-viral olfactory dysfunction. The workflow shifts away from anatomical intervention. Management may include a trial of olfactory training, counseling the patient on safety measures (e.g., smoke and gas detectors), and continued observation. If other subtle neurologic signs develop over time, a follow-up with Neurology to consider an underlying neurodegenerative process may be warranted.

If the study is indeterminate, showing subtle, nonspecific findings, the next step may involve discussion with the radiologist, clinical correlation with laboratory tests for inflammatory markers, or a follow-up scan in 3-6 months to assess for any change.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup for anosmia requires avoiding several common pitfalls. First, do not mistake a standard “MRI head” for the targeted study; always specify “MRI orbits, face, and neck” with and without contrast to ensure the correct protocol is performed. Second, avoid attributing new, persistent anosmia in an older adult to “just aging” without a proper workup, as this can delay the diagnosis of a treatable intracranial mass. Finally, forgoing contrast in an MRI for a suspected tumor or inflammatory process severely limits the diagnostic utility of the exam.

If the patient presents with anosmia accompanied by any “red flag” symptoms—such as visual changes, severe headache, seizures, or other cranial nerve deficits—escalate care immediately with an urgent referral to Neurology or the emergency department for expedited evaluation.

Related ACR Topics and Tools

For a comprehensive overview of imaging for all cranial nerve pathologies, this depth piece is best used alongside its parent topic article. The tools below can help you select the right study and understand its technical basis for this and other clinical scenarios.

Frequently Asked Questions

Is a CT scan ever the right first choice for anosmia?

According to the ACR, a maxillofacial CT (rated ‘May be appropriate’) can be a reasonable first test if your clinical suspicion is almost exclusively for uncomplicated sinonasal disease, like chronic rhinosinusitis. However, if there is any concern for an intracranial cause or the diagnosis is unclear, MRI is the superior initial study due to its excellent soft-tissue resolution for evaluating the olfactory nerves and brain.

Why is a standard MRI of the head not sufficient?

A standard ‘MRI head’ protocol is optimized for the brain parenchyma but often uses thicker slices and may not include the specific high-resolution coronal sequences needed to visualize the very small olfactory bulbs and tracts. The dedicated ‘MRI orbits, face, and neck’ protocol ensures these structures are imaged appropriately, reducing the risk of missing subtle pathology in the anterior cranial fossa.

Does the workup change if the anosmia is from a known head trauma?

Yes, the clinical context is key. In post-traumatic anosmia, the primary goal is often to identify skull base fractures, particularly involving the cribriform plate. A non-contrast high-resolution CT of the facial bones and skull base is often the initial imaging modality of choice in the acute setting. MRI may be used later to assess for direct injury to the olfactory bulbs, such as contusion or shearing.

What if my patient cannot have an MRI with contrast due to a gadolinium allergy or renal failure?

If IV contrast is contraindicated, an ‘MRI orbits, face, and neck without IV contrast’ is still rated as ‘May be appropriate’ and is more informative for soft tissues than a CT. While it cannot assess for abnormal enhancement, it can still detect masses based on morphology and T2 signal, as well as evaluate for olfactory bulb atrophy and sinus disease. This is a reasonable alternative when contrast cannot be administered.

My patient’s anosmia started after a COVID-19 infection. Do they still need an MRI?

Post-viral olfactory dysfunction, particularly after COVID-19, is very common and is often a clinical diagnosis that does not require imaging, especially if symptoms are improving. However, imaging should be considered if the anosmia is unusually severe, prolonged (e.g., lasting more than 6-12 months without improvement), or accompanied by other atypical neurologic symptoms, to rule out an alternative underlying cause.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 26, 2026