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What Is the Best Imaging Modality to Investigate Olfactory
Dysfunction in the Setting of Normal Endoscopy?
Thomas S. Higgins, MD, MSPH; Andrew P. Lane, MD
Key Words: Olfaction, anosmia, hyposmia, imaging, computed tomography, magnetic resonance imaging.
Laryngoscope, 124:4–5, 2014
BACKGROUND
LITERATURE REVIEW
Olfactory dysfunction is a common complaint worldwide. The workup typically includes a detailed history
and physical examination, chemosensory tests, and
imaging studies. Olfactory dysfunction may be broadly
divided into two categories: conductive and sensorineural. Examples of conductive etiologies include sinonasal
inflammatory disease or obstructive sinonasal masses,
whereas sensorineural causes include post-upper respiratory infections (post-URI); traumatic, iatrogenic,
aging, neurodegenerative diseases (e.g., Alzheimer’s or
Parkinson’s disease); and toxic exposure. When the history, physical examination, and nasal endoscopy are
indicative of sinonasal disease or a mass, computed tomography (CT) of the sinus is typically performed, and
the patient’s olfactory dysfunction is managed by treating the underlying disease. A subset of patients,
however, present with nonspecific historical, physical examination, or nasal endoscopic findings, which fail to
reveal a definitive etiology for the olfactory dysfunction.
Imaging studies are generally recommended in these
cases; however, there is uncertainty among otolaryngologists as to which imaging studies are necessary to fully
evaluate the etiology of olfactory dysfunction. This
review describes the evidence-based decision-making
process for using imaging studies to evaluate olfactory
dysfunction in this setting.
A study of 750 subjects evaluated from 1980 to 1986
at the University of Pennsylvania Smell and Taste Center
described the etiologic characteristics of their patient
sample. The most common etiologies for olfactory dysfunction seen at the center include post-upper respiratory
infection (26%), idiopathic (22%), head trauma (18%), and
nasal and paranasal sinus disease (15%). The incidence of
a brain tumor in their sample was only 0.3%. The authors
made no specific recommendations regarding imaging.1
Because this study evaluated a sample from a highly specialized center that receives many referrals from
otolaryngologists, the incidence of etiologies is not likely
generalizable to the general population or to a sample
seen in the general otolaryngologist’s clinic. Paranasal
sinus disease and brain/nasal tumors may represent a
larger percentage of patients with olfactory dysfunction,
as the general otolaryngologist can often readily diagnose
these conditions and generally does not refer them to a
subspecialist smell and taste center.
A study of 1,000 subjects seen at the Nasal Dysfunction Clinic in San Diego demonstrated that inflammatory
processes were the etiology of olfactory dysfunction in the
vast majority of their patient sample (61.3%), followed by
postviral (16.6%) and head trauma (8.7%). These three
entities represented 86.6% of cases of olfactory dysfunction. Their workup comprised of history and physical
examination, nasal endoscopy, smell identification testing,
and CT of the sinuses in every patient. Patients were diagnosed with postviral cause if the history demonstrated a
temporal relationship with the olfactory dysfunction and
no inflammatory disease was noted on the CT scan; no
further imaging was obtained in these patients.2 This
study did not indicate the incidence of tumors or neurodegenerative processes in the sample or if any patient
underwent neuroimaging such as magnetic resonance
imaging (MRI). These two studies have the largest sample
sizes of subjects to evaluate olfactory dysfunction. Studies
with smaller cohorts of patients have been published.
A few review articles have been published addressing imaging in olfactory dysfunction. A review by the
From the Kentuckiana Ear, Nose, and Throat, PSC (T.S.H.) and
Department of Surgery (T.S.H.), Division of Otolaryngology–Head and
Neck Surgery, University of Louisville, Louisville, Kentucky; and the
Department of Otolaryngology–Head and Neck Surgery (A.P.L.), Johns
Hopkins University School of Medicine, Baltimore, Maryland, U.S.A.
Editor’s Note: This Manuscript was accepted for publication
October 24, 2012.
The authors have no funding, financial relationships, or conflicts
of interest to disclose.
Send correspondence to Andrew P. Lane, MD, Department of Otolaryngology–Head and Neck Surgery, Johns Hopkins Outpatient Center,
6th Floor, 601 N. Caroline Street, Baltimore, MD 21287-0910. E-mail:
[email protected]
DOI: 10.1002/lary.23892
Laryngoscope 124: January 2014
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Higgins and Lane: Imaging Modality for Olfactory Dysfunction
TABLE I.
Historical Findings in Patients With Olfactory Dysfunction With Corresponding Potential Diagnoses and Recommended Imaging Modalities.
Finding
Upper respiratory infection at onset
Potential Diagnoses
Post-URI hyposmia/anosmia
Recommended Imaging Modality
CT scan of sinuses
Head trauma
Traumatic olfactory nerve sheering injury
CT scan of sinuses
After sinus surgery
Family history of neurogenerative disease
Iatrogenic or recurrent sinusitis
Alzheimer’s, Parkinson’s, Huntington’s
CT scan of sinuses
MRI brain or other neuroimaging study
Other neurologic deficits (motor
or cognitive deficits,
headaches, vision impairment)
CVA, intracranial tumor,
neurogenerative process, schizophrenia
MRI brain or other neuroimaging study
Olfactory hallucinations
Temporal lobe mass or process, schizophrenia
MRI brain or other neuroimaging study
Hypogonadism or lifelong anosmia
Congenital etiology (e.g., Kallman’s
syndrome, encephalocele)
MRI brain or other neuroimaging study
CT ¼ computed tomography; CVA ¼ cerebrovascular accident; MRI ¼ magnetic resonance imaging; URI ¼ upper respiratory infection.
group at the University of Pennsylvania in 1993 described
neuroimaging findings that are found with several disorders related to olfactory dysfunction, including
Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Korsakoff’s psychosis, schizophrenia, congenital
disorders (Kallman’s syndrome), and head trauma.3 A
more recent review described imaging techniques, pathological findings, and provided a clinically based strategy
for choice of imaging. The authors’ opinion was that most
patients can be screened with a CT scan without contrast
of the sinuses; however, some patients with infectious or
postinfectious causes of anosmia in ‘‘the appropriate clinical scenario’’ may undergo an MRI scan through the
frontal lobes to ‘‘identify acute or chronic sequel of infectious neuritis or herpes encephalitis.’’ They recommended
MRI with and without gadolinium when a neoplastic process was suspected; however, the authors did not indicate
the findings suspicious for such processes or describe if an
MRI would be recommended when the history, examination, endoscopy, and CT scan were negative. The authors
did mention that olfactory meningiomas usually do not
invade into the nasal cavity and thus could be missed
without an MRI. However, olfactory meningiomas typically do not present as anosmia, as the gradual process of
olfactory dysfunction often goes unnoticed, and instead
present with other neurogenic deficits such as headache,
cognitive and motor deficits, and vision impairment.4
BEST PRACTICE
The etiology of most cases of olfactory dysfunction
can be identified, or at least suggested, by history, physical
examination, and endoscopy. Some authors recommend a
CT scan of the sinuses to screen for inflammatory and obstructive processes regardless of presentation, whereas
some authors recommend a more selective imaging evaluation. In cases of historical evidence as well as signs and
symptoms that suggest paranasal sinus disease, trauma,
iatrogenic, and post-URI etiologies, a noncontrast CT scan
of the sinuses appears sufficient for evaluation. When endoscopy identifies a sinonasal tumor, imaging is tailored to
the tumor type and extent. In a patient with a negative
endoscopy, the choice of imaging is somewhat controversial. Based on expert opinions and large prospective
cohort studies, the choice of imaging modality for evaluation of olfactory dysfunction in patients without
endoscopic findings of sinonasal disease, masses, or other
visualized etiologies for the olfactory dysfunction depends
Laryngoscope 124: January 2014
of the patient demographics and history. In general, the
practitioner uses imaging to evaluate for either: 1) a neurogenic/sensory etiology, or 2) intracranial tumor or other
obstructive process not identified on endoscopy. Although
an MRI scan in the setting of olfactory dysfunction without an identifiable etiology may rarely identify a tumor
(0.3% in the University of Pennsylvania series), there are
no large cohort studies or cost-effectiveness studies to
evaluate this scenario. Table I outlines potential components of the history and physical examination that may
compel the physician to consider imaging. A patient, for
example, with a family history of a neurodegenerative disorder and with neurologic symptoms, such cognitive
impairment or motor deficits, may benefit from an MRI of
the brain to detect findings of a neurodegenerative disorder such as Alzheimer’s, Parkinson’s, Huntington’s, or
Korsakoff’s psychosis. It should be noted, however, that olfactory dysfunction also occurs as a natural process in
aging. Among people over the age of 80 years, up to 60%
to 80% demonstrate an impaired sense of smell, and 50%
have anosmia in some studies.5 The patient with a history
of hypogonadism and/or anosmia for a lifetime should
undergo MRI evaluation for congenital agenesis of the olfactory bulbs or Kallman’s syndrome. Patients with
olfactory hallucinations should be evaluated with MRI of
the brain to evaluate for temporal lobe processes.
Future research should include cost-effectiveness
studies and further population-based studies to clarify
the incidences of etiologies for olfactory dysfunction.
LEVEL OF EVIDENCE
The evidence for choosing an imaging modality for
evaluation of olfactory dysfunction in the setting of normal history, physical examination, and nasal endoscopy
includes individual case series (level 4) and expert opinion (level 5).
BIBLIOGRAPHY
1. Deems DA, Doty RL, Settle RG, et al. Smell and taste disorders, a study of
750 patients from the University of Pennsylvania Smell and Taste Center. Arch Otolaryngol Head Neck Surg 1991;117:519–528.
2. Harris R, Davidson TM, Murphy C, Gilbert PE, Chen M. Clinical evaluation and symptoms of chemosensory impairment: one thousand consecutive cases from the Nasal Dysfunction Clinic in San Diego. Am J Rhinol
2006;20:101–108.
3. Li C, Yousem DM, Doty RL, Kennedy DW. Neuroimaging in patients with
olfactory dysfunction. AJR Am J Roentgenol 1994;162:411–418.
4. Hamilton BE, Weissman JL. Imaging of chemosensory loss. Otolaryngol
Clin North Am 2004;37:1255–1280.
5. Lafreniere D, Mann N. Anosmia: loss of smell in the elderly. Otolaryngol
Clin North Am 2009;42:123–131.
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