What is the recommended approach for evaluating phantom smells?

Evaluation of Phantom Smells (Phantosmia)

Most patients with phantom smells do not require imaging unless history or physical examination reveals concerning features; the evaluation 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

Initial Clinical Assessment

History and Physical Examination

• Determine the pattern of phantosmia: Distinguish between unirhinal (one nostril) versus birhinal (both nostrils) presentation, as these represent different clinical syndromes 2
• Assess for temporal lobe dysfunction: Olfactory hallucinations may indicate temporal lobe pathology, degenerative disease, or psychiatric conditions 1
• Evaluate for associated symptoms: Check for concurrent hyposmia, headaches, or neurological symptoms that may suggest underlying pathology 3
• Perform rigid nasal endoscopy: This differentiates between conduction loss from sinonasal obstruction, inflammatory causes, and potential tumors 1

Psychophysical Testing

• Conduct standardized olfactory testing using validated instruments like UPSIT or Sniffin'Sticks to objectively characterize olfactory function 1, 4
• Testing is mandatory if there is any olfactory complaint, regardless of endoscopic findings 1

When to Pursue Imaging

Indications for Advanced Imaging

• Discordance between subjective symptoms and endoscopic findings raises suspicion for sinonasal or skull base tumors not visible on endoscopy 1
• Persistent or progressive symptoms without clear inflammatory or obstructive cause 1
• Associated neurological signs suggesting central nervous system pathology 1

Imaging Modality Selection

• MRI orbits, face, and neck is the mainstay for directly imaging the olfactory apparatus, sinonasal structures, and anterior cranial fossa tumors 1
• 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
• Contrast-enhanced CT is appropriate for suspected granulomatous or neoplastic disease 1
• CT head, CTA head, and MRA head have no role in olfactory nerve evaluation 1

Common Etiologies to Consider

Peripheral Causes

• Sinonasal inflammatory disease: Rhinosinusitis, nasal polyposis causing conduction loss 1
• Trauma, aging, upper respiratory infections: Most common causes of olfactory impairment 1
• Tumors: Squamous cell carcinomas, meningiomas, esthesioneuroblastoma affecting the cribriform plate 1
• Inflammatory lesions: Sarcoidosis, granulomatosis with polyangiitis 1

Central Causes

• Neurodegenerative disorders: Alzheimer disease, Parkinson disease, Lewy body dementia 1, 3
• Temporal lobe dysfunction: May cause olfactory hallucinations distinct from peripheral phantosmia 1
• Psychiatric conditions: Depression and other mood disorders 1

Clinical Pitfalls

• Do not assume all phantosmia requires imaging: Most cases do not need advanced imaging unless clinical examination warrants it 1
• Recognize unirhinal cyclic phantosmia as a distinct syndrome: This can be initiated by coughing, sneezing, or vigorous nasal breathing and may respond to GABAergic medications 5, 2
• Consider neurodegenerative disease: Phantosmia, particularly when associated with headaches, may herald Lewy body dementia or other neurodegenerative conditions 3
• Avoid ordering CT head or vascular imaging: These modalities have no established role in olfactory evaluation 1