Embryology and Clinical Development of the Human Olfactory System

Harvey B. Sarnat; Laura Flores-Sarnat

doi:10.1055/s-0042-1758471

Journal of Pediatric Neurology, Table of Contents

Journal of Pediatric Neurology 2024; 22(01): 001-007
DOI: 10.1055/s-0042-1758471

Review Article

Embryology and Clinical Development of the Human Olfactory System

Harvey B. Sarnat

¹Department of Paediatrics, University of Calgary Cumming School of Medicine and Alberta Children's Hospital Research Institute (Owerko Centre), Calgary, Alberta, Canada

²Department of Pathology and Laboratory Medicine (Neuropathology), University of Calgary Cumming School of Medicine and Alberta Children's Hospital Research Institute (Owerko Centre), Calgary, Alberta, Canada

³Department of Clinical Neurosciences, University of Calgary Cumming School of Medicine and Alberta Children's Hospital Research Institute (Owerko Centre), Calgary, Alberta, Canada

,

Laura Flores-Sarnat

¹Department of Paediatrics, University of Calgary Cumming School of Medicine and Alberta Children's Hospital Research Institute (Owerko Centre), Calgary, Alberta, Canada

³Department of Clinical Neurosciences, University of Calgary Cumming School of Medicine and Alberta Children's Hospital Research Institute (Owerko Centre), Calgary, Alberta, Canada

› Author Affiliations

Abstract

The olfactory system is unique as a special sensory system in its developmental neuroanatomy and function. Neonatal olfactory reflexes can be detected in the fetus from 30 weeks gestation and can be tested in term and preterm neonates and older children. Most efferent axons from the olfactory bulb terminate in the anterior olfactory nucleus within the olfactory tract, with secondary projections to the amygdala, hypothalamus, hippocampus, and entorhinal cortex (parahippocampal gyrus), with tertiary projections also to the insula and other cortical regions. The olfactory bulb and tract incorporate an intrinsic thalamic equivalent. The olfactory bulb may be primary in generating olfactory auras in some cases of temporal lobe epilepsy. Developmental malformations may involve the olfactory bulb and tract, isolated or as part of complex cerebral malformations and genetic syndromes. Primary neural tumors may arise in the olfactory bulb or nerve. Impaired olfaction occurs in neonatal hypoxic/ischemic and some metabolic encephalopathies. Loss of sense of smell are early symptoms in some neurodegenerative diseases and in some viral respiratory diseases including coronavirus disease 2019. Testing cranial nerve I is easy and reliable at all ages, and is recommended in selected neonates with suspected brain malformations or encephalopathy.

Keywords

olfactory development - auras - malformations - encephalopathies

Full Text

References

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