Agnosias: recognition disorders in patients with brain tumors.

Two main varieties of recognition disorders are distinguished in neuropsychology: agnosias and semantic disorders. The term agnosias is generally used to denote recognition defects limited to a single perceptual modality (which is itself apparently intact), whereas the term semantic disorders is used to denote recognition defects involving all the sensory modalities in a roughly similar manner. Brain tumors can be one of the aetiologies underlying agnosias and semantic disorders. However, due to the heterogeneity and the rarity of recognition disorders, their investigation can be useful only to suggest or exclude the oncological nature of a brain lesion, but not to systematically monitor the clinical outcome in tumor patients. Furthermore, the relevance of recognition disorders as a hint toward a diagnosis of brain tumor varies according to the type of agnosia and of semantic disorder and the localization of the underlying brain pathology. The hypothesis that a variety of agnosia (or of semantic disorder) may be due to a neoplastic lesion can, therefore, be advanced if it is consistent with our knowledge about the usual localization and the growing patterns of different types of brain tumors.