A Comparative Study of Brain Perfusion Single-Photon Emission Computed Tomography and Magnetic Resonance Imaging in Patients with Post-traumatic Anosmia

Abstract

Background Loss of smell is a problem that can occur in up to 30% of patients with head trauma. The olfactory function investigation methods so far in use have mostly relied on subjective responses given by patients. Recently, some studies have used magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT) to evaluate patients with post-traumatic anosmia. The present study seeks to detect post-traumatic anosmia and the areas in the brain that are related to olfactory impairment by using SPECT and MRI as imaging techniques. Methods The study was conducted on 21 patients suffering from head injury and consequently anosmia as defined by an olfactory identification test. Two control groups (traumatic normosmic and nontraumatic healthy individuals) were selected. Brain MRI, qualitative and semiquantitative SPECT with 99mtc-ethyl-cysteinate-dimer were taken from all the patients. Then the brain SPECT and MRI were compared with each other. Results Semi-quantitative assessment of the brain perfusion SPECT revealed frontal, left parietal, and left temporal hypoperfusion as compared with the two control groups. Eighty-five percent of the anosmic patients had abnormal brain MRI. Regarding the MRI, the main abnormality proved to be in the anterior inferior region of the frontal lobes and olfactory bulbs. Conclusions The findings of this study suggest that damage to the frontal lobes and olfactory bulbs as shown in the brain MRI and hypoperfusion in the frontal, left parietal, and left temporal lobes in the semiquantitative SPECT corresponds to post-traumatic anosmia. Further neurophysiological and imaging studies are definitely needed to set the idea completely.

Olfactory and executive dysfunctions following orbito-basal lesions in traumatic brain injury

“…In contrast to previous studies, this study was only able to confirm a marginally significant association between posttraumatic temporal lesions and olfactory dysfunction when applying the Bonferroni adjustment [14,15,32]. Perhaps this was due to the low number of patients in the left and right temporal lesion groups (n ¼ 11 and 14).…”

“…These effects were strongest in pre-frontal regions and weaker in the temporal lobe [14]. When using SPECT to investigate brain activity in posttraumatic anosmia, researchers found reduced perfusion in frontal, left parietal and left temporal regions [15]. Another study confirmed reduced metabolism in the median prefrontal cortex and the orbitofrontal cortex of patients with posttraumatic anosmia [16].…”

Posttraumatic olfactory dysfunction

“…Other imaging modalities such as single-photon emission computed tomography (SPECT) and positron-emission tomography (PET) have been investigated in patients with olfactory dysfunction with promising findings [62][63][64]. However as they were not used in patients whose loss was specifically posttraumatic loss the diagnostic role of these tests remains to be elucidated.…”

Anosmia and hyposmia

“…16 A role for direct brain injury is also supported by many studies showing abnormalities on MRI in frontal lobes as well as olfactory bulbs, and a recent study with single-photon emission CT even demonstrated hypoperfusion of parietal and temporal lobes in patients with posttraumatic anosmia compared with patients with similar trauma but normal sense of smell. 15 Local exposures to toxins such as ammonia, gasoline, hairdressing chemicals, and others can cause permanent smell dysfunction. 18 Adverse reactions to pharmaceuticals can also cause toxic damage to the olfactory function, both systemically 19 (especially with chemotherapy) and local, such as the cases of anosmia found to be caused by the topical application of intranasal preparations containing zinc, which were marketed as a treatment for upper respiratory infections.…”