The olfactory cleft is a specialized anatomical space within the nasal cavity that plays a direct role in the sense of smell. This narrow region houses the primary sensory tissue responsible for detecting airborne odor molecules. Understanding this area helps comprehend how we perceive scents and how conditions can affect this ability. Its integrity and accessibility are directly linked to effective olfactory function.
Anatomy and Role in Smell
The olfactory cleft is a paired space located in the upper and medial parts of the nasal cavity. It is bounded medially by the perpendicular plate of the ethmoid bone and laterally by the vertical portion of the basal lamella of the middle turbinate. The cribriform plate and superior turbinate define its superior boundary, while the inferior margin of the middle turbinate forms its lower limit. This narrow area, approximately 1–2 mm wide, contains the olfactory epithelium, a specialized neuroepithelium about 60 µm thick that covers an area of roughly 200 to 400 mm².
Odorants, or scent molecules, reach the olfactory cleft and epithelium through airflow from the front of the nose or the back of the throat. Once odorants dissolve in the mucus layer covering the epithelium, they interact with specific receptors located on cilia of olfactory sensory neurons. These neurons are bipolar cells with dendrites extending to the epithelial surface and axons projecting upwards through the cribriform plate to synapse in the olfactory bulb, which is part of the brain. This interaction triggers a biochemical reaction and an electrical signal, which is then transmitted to the brain for interpretation as a specific smell.
Common Issues Affecting the Olfactory Cleft
Various conditions can affect the olfactory cleft, leading to impaired smell, such as hyposmia (reduced smell) or anosmia (complete loss of smell). Inflammation, often stemming from chronic rhinosinusitis, is a common cause, as it can block odorants from reaching the olfactory epithelium. This obstruction can be due to mucosal edema or the presence of inflammatory mediators directly affecting the olfactory neurons.
Nasal polyps, benign inflammatory growths, frequently develop in the sinonasal cavities and can obstruct the olfactory cleft, preventing odor molecules from reaching receptors. These polyps, particularly those medial to the middle turbinate, are strongly associated with olfactory dysfunction. In some cases, a benign glandular neoplasm called respiratory epithelial adenomatoid hamartoma (REAH) can also form in the olfactory cleft, presenting as polypoid masses that can cause obstruction. Structural abnormalities, such as those seen in unilateral cleft lip nasal deformities, can also alter airflow to the olfactory cleft, impacting the sense of smell.
Identifying and Addressing Olfactory Cleft Problems
Healthcare professionals use several methods to diagnose issues within the olfactory cleft. Nasal endoscopy allows for direct visual examination of the nasal cavity and the olfactory cleft to identify any obstructions or abnormalities. Imaging techniques, such as computed tomography (CT) scans and magnetic resonance imaging (MRI), provide detailed information on the cleft’s conformation, its relationship to adjacent structures, and can detect inflammation, polyps, or tumors. CT scans, in particular, can show the extent of olfactory cleft opacification, which correlates with the severity of olfactory dysfunction.
Addressing olfactory cleft problems often involves treating the underlying cause to restore airflow and function. Medical management typically includes corticosteroids, administered orally or topically, to reduce inflammation and shrink polyps, particularly in chronic rhinosinusitis. If medical therapy is ineffective or if there are significant obstructions like large polyps or tumors, surgical interventions may be considered. Endoscopic sinus surgery, for instance, can remove polyps or other masses, aiming to clear the olfactory cleft and improve patency.