Impairment of olfactory recognition after closed head injury.

To investigate the effects of closed head injury (CHI) on olfactory identification, we administered a test of olfactory naming and forced choice recognition to 52 CHI patients who had no evidence of anosmia. The Olfactory Identification Test consisted of 'scratch and sniff' labels of familiar nonirritant odorants. In comparison with a normal control group (n = 19) of similar age, olfactory naming and recognition were impaired in the CHI series, particularly in patients with moderate or severe head injury. The presence of a haematoma or contusion in the frontal/temporal region was also related to impaired olfactory recognition. We suggest that nonmissile head injury can produce at least a partial impairment of olfactory recognition despite relatively preserved olfactory detection.