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Objective.—To report the first example of an abnormal magnetic resonance imaging (MRI) test in a patient with migraine and olfactory hallucinations and to provide additional evidence for a possible role of the temporal lobe in migraine.
Background.—The relationship between the temporal lobe and migraine with or without hallucinations is unclear and continues to evolve. Clinical and functional neuroimaging studies (positron emission tomography/single photon emission computed tomography) have lent support to the possibility of a relationship. Anatomical neuroimaging with computed tomography has previously been normal.
Methods.—The history and findings of an adolescent with migraine and olfactory hallucinations is reported.
Results.—Brain MRI demonstrated a mass in the temporal lobe.
Conclusions.—Magnetic resonance imaging should be considered in patients with olfactory hallucinations and migraine. In addition, the role of the temporal lobe in migraine warrants further study.
Visual hallucinations are a common aura in migraine. Other types of hallucinations, such as auditory and olfactory, can occur but are rare. Olfactory hallucinations have been reported in patients with migraine in whom brain computed tomography (CT) has yielded normal findings. 1-5 The results of magnetic resonance imaging (MRI) have not been described in these patients.
This is the first report of abnormal neuroimaging in a patient with olfactory hallucinations during migraine. Magnetic resonance imaging demonstrated a mass lesion in the temporal lobe.
A 16-year-old adolescent boy presented with a 2-year history of severe, unilateral, primarily left temporal, “pounding” headache associated with nausea, vomiting, phonophobia, photophobia, and left-sided numbness. The duration of the headache was typically several hours. The only visual symptom was occasional blurry vision. The headaches were relieved by sleep. The patient reported rare olfactory sensations of smelling “burnt wood,” which occurred during or after the headache, not as an aura, and lasted seconds to minutes. During these olfactory experiences, he would query others to determine whether they were aware of the same smell. His family history was positive for migraine in his mother. The findings of neurological and funduscopic examination were normal. All three items from the “Pocket Smell Test” were correctly identified. The results of an electroencephalogram (EEG) were normal. Magnetic resonance imaging demonstrated a circular mass, 1.9 × 1.8 cm, in the left posterior temporal area with a heterogeneous appearance (primarily hypointense to the brain on T1-weighted images but more heterogeneous with some areas of isointensity on PD (proton density)-weighted images and T2-weighted images) (Figure 1). There was no contrast enhancement with gadolinium. The adjacent cisterns were minimally enlarged. The findings of a follow-up MRI 3 months later were unchanged. The patient had partial relief with aspirin, no relief with indomethacin, and developed side effects with propranolol. Valproic acid was recommended but refused. Ongoing care was erratic; the patient was eventually lost to follow-up 1 year later.
Previous reports of olfactory hallucinations with migraine are rare and have described a variety of smells that can be either pleasant or unpleasant. Such hallucinations may not be so rare but, rather, they may be disturbing to the patient and not readily disclosed. Often the smell is one of burning, such as that of cookies, wood, rubber, or smoke (eg, cigarettes, cigars). 2-5 Some examples of olfactory hallucinations with migraine might represent osmophobia or hyperosmia of real odors rather than a hallucination. 6 In our patient, the sensation of smelling burnt wood was dramatic, was readily disclosed by him, was not experienced by others with him at the time, and most probably represented a hallucination.
Temporal lobe involvement has been reported in migraine, although the specific role and pathophysiology remain speculative. It is well known that migraine occurs more frequently in patients with seizures, especially of the complex partial (ie, temporal lobe) variety. In addition, several disorders that are putative migraine equivalents, such as cyclic vomiting and transient global amnesia, have been associated with both vasomotor changes as well as spreading depression in the temporal lobe. 7,8 Temporal lobe phenomenona can occur during the aura phase of a migraine attack. 9 A middorsal temporal lobe glioma has been reported in a patient with migraine and a typical visual aura. 10 This patient's EEG, although not demonstrating epileptiform changes, did show temporal lobe slowing.
This case provides additional support for temporal lobe involvement in migraine. One theory suggests that sensitivity to cortically (eg, temporal lobe) generated internal and external stimuli, such as emotion, stress, or other afferent precipitants (eg, olfactory), can subsequently trigger neurovascular projections associated with the locus ceruleus, the nucleus raphae dorsalis, and the trigeminovascular reflex. 11
The underlying pathophysiology for olfactory hallucinations in migraine is also not fully understood. When they occur during a seizure, both temporal lobe and orbitofrontal regions have been implicated. 12 In migraine, spreading depression of the temporal lobe is a possible explanation, especially when the hallucination occurs as an aura. 11 Anterior progression of hypoperfusion to involve the temporal lobe from the occipital lobes, consistent with spreading depression, has been demonstrated during (our italics) migraine in a patient without aura. 13 The demonstration of this phenomenon after the onset of migraine suggests that spreading depression involving the temporal lobe is a reasonable explanation when the olfactory hallucination occurs during a migraine, as in our patient.
Without knowledge of the histopathology, we cannot definitively characterize the nature of the MRI lesion. Although the hypointense signals suggest cystic characteristics, the mass had a component that was isointense to the brain. The surrounding sulci were minimally enlarged, suggesting that the lesion might be developmental in nature such as a temporal lobe cyst or hamartoma. Although the patient did not develop any other symptoms during the 1-year follow-up, and a repeat MRI 3 months later was unchanged in appearance, the possibility of a benign neoplastic lesion, such as a ganglioglioma, cannot entirely be ruled out.
Finally, the possibility that our patient's olfactory hallucinations and headaches were manifestations of complex partial seizures, historically referred to as “uncinate fits,” cannot be completely excluded. Olfactory epileptic auras are rare, accounting for approximately 0.9% of all epileptic auras. 12 Typically, they are unpleasant experiences, occur with other epileptic auras, and evolve into a more definite manifestation of a seizure. In addition, headache is a common postictal symptom, although it rarely occurs as an epileptic manifestation. 14 When reported, it is frequently described as a nonpainful “pressure,”“swelling,” or “fullness” sensation. Several factors weigh against the headache and olfactory hallucinations being manifestations of seizures in our patient: the headaches were severely painful and had typical migraine characteristics, there was neither loss nor alteration of consciousness, there was no evolution into a more definite epileptic seizure despite the duration of the episodes, and the EEG was normal.
Because MRI is more sensitive than CT for temporal lobe lesions, it should be considered in those rare patients with migraine and olfactory hallucinations. Further study of the specific relationship of the temporal lobe, migraine, and hallucinations is needed to delineate the role of cortical, brain stem, and vascular structures in migraine.