Evaluation of Phantom Smells (Phantosmia)

Initial Clinical Assessment

The American College of Radiology recommends that the evaluation of patients with phantom smells should begin with thorough nasal endoscopy and psychophysical olfactory testing, with MRI orbits/face/neck reserved for cases where findings don't correlate or when structural pathology is suspected 1, 2
Assessing for temporal lobe dysfunction is crucial, as olfactory hallucinations may indicate temporal lobe pathology, degenerative disease, or psychiatric conditions 1, 2
Rigid nasal endoscopy should be performed to differentiate between conduction loss from sinonasal obstruction, inflammatory causes, and potential tumors 3, 4
Standardized olfactory testing using validated instruments like UPSIT or Sniffin'Sticks should be conducted to objectively characterize olfactory function 3, 4, 5

Imaging should be pursued when there is discordance between subjective symptoms and endoscopic findings, raising suspicion for sinonasal or skull base tumors not visible on endoscopy 3, 4
Persistent or progressive symptoms without clear inflammatory or obstructive cause, or associated neurological signs suggesting central nervous system pathology, are indications for imaging 1, 2
MRI orbits, face, and neck is the mainstay for directly imaging the olfactory apparatus, sinonasal structures, and anterior cranial fossa tumors 1, 2
Pre- and post-contrast MRI provides the best opportunity to identify and characterize lesions affecting the olfactory pathway 1
CT maxillofacial is useful specifically for evaluating fractures, paranasal sinus inflammatory disease, and bony anatomy 1, 2

Sinonasal inflammatory disease, such as rhinosinusitis and nasal polyposis, can cause conduction loss 1, 2
Trauma, aging, and upper respiratory infections are common causes of olfactory impairment 1, 2
Tumors, such as squamous cell carcinomas, meningiomas, and esthesioneuroblastoma, can affect the cribriform plate 1, 2
Inflammatory lesions, such as sarcoidosis and granulomatosis with polyangiitis, can also cause olfactory impairment 1, 2
Neurodegenerative disorders, such as Alzheimer disease, Parkinson disease, and Lewy body dementia, can cause central phantosmia 1, 2

The American College of Radiology advises against assuming all phantosmia requires imaging, as most cases do not need advanced imaging unless clinical examination warrants it 1, 2
CT head or vascular imaging has no established role in olfactory evaluation and should be avoided 1, 2

Recent upper respiratory infections, such as COVID-19, can cause qualitative olfactory disorders, including phantosmia, in patients with a history of infection 6, 7, 8
Rigid nasal endoscopy is essential to differentiate conduction loss from sinonasal obstruction, inflammatory disease, or tumors, and should be performed in conjunction with standardized olfactory testing, such as UPSIT or Sniffin'Sticks, to objectively characterize olfactory function 9

Olfactory training should be offered for post-infectious olfactory dysfunction, including COVID-19 cases, due to its simplicity and safety, and has been shown to be effective in improving olfactory function 6, 7

Recent upper‑respiratory infections, especially COVID‑19, have driven a marked increase in qualitative olfactory disorders such as phantosmia, making a recent viral illness a key historical element to assess. 10
Traumatic injury to the olfactory nerve is the most common cause of post‑traumatic phantosmia, so a detailed trauma history is essential. 11
Neurological symptoms that suggest temporal‑lobe dysfunction or early neurodegenerative disease (e.g., Alzheimer’s, Parkinson’s) should prompt evaluation for central causes of phantosmia. 11

When structural pathology is suspected, magnetic resonance imaging of the orbits, face, and neck—with and without contrast—is the preferred modality to identify central or peripheral lesions. 12
Computed tomography of the maxillofacial region is useful specifically for assessing facial fractures, paranasal sinus inflammatory disease, and bony anatomy, but has no routine role in olfactory evaluation. [11][12]

Peripheral causes – Post‑infectious olfactory dysfunction, including that following COVID‑19, is a leading peripheral etiology of phantosmia. 10
Central causes – Temporal‑lobe pathology such as tumors or epilepsy requires neurological work‑up because it can produce unilateral phantosmia with ipsilateral olfactory loss. 11

Post‑infectious (including COVID‑19) phantosmia – Olfactory training is recommended as first‑line therapy because it is safe, simple, and has demonstrated efficacy in restoring normal smell perception. 10
Safety counseling for patients with phantosmia should include installation of smoke and gas alarms, careful monitoring of food expiration dates, and cautious cooking practices to prevent hazardous exposures. 10
For persistent or refractory phantosmia, topical nasal medications may be employed, although evidence for systemic pharmacologic therapy remains limited. 10

After the acute phase of post‑infectious phantosmia, patients should receive routine rhinology follow‑up to monitor recovery and adjust management as needed. 10
Magnetic resonance imaging should be reconsidered only if new concerning neurological symptoms arise or if the phantosmia lacks a clear temporal link to a prior viral infection. 10

Do not overlook temporal‑lobe pathology in patients with persistent olfactory hallucinations, as this may indicate serious central nervous system disease. 11