Keros classification of olfactory fossa
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View Arlene Campos's current disclosures- Keros classification of the olfactory fossa
- Keros classification
The Keros classification is a method of classifying the depth of the olfactory fossa.
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Usage
The Keros classification remains widely used, although its simplicity has been criticized, and alternative classifications have been proposed (e.g. Gera classification and Thailand-Malaysia-Singapore (TMS) classification) 5,6
Local anatomy
The ethmoid labyrinth is covered by the fovea ethmoidalis of the frontal bone and separates the ethmoidal cells from the anterior cranial fossa.
The very thin horizontal cribriform plate (lamina cribrosa) of the ethmoid bone separates the olfactory fossa (or groove) of the anterior cranial fossa above from the olfactory cleft of the nasal cavity below.
The olfactory groove is bounded laterally by the vertical lateral lamella, which extends from the fovea ethmoidalis to the cribriform plate and medially by the crista galli. It contains the olfactory bulb and the anterior ethmoidal artery 5.
Classification
The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate and is grouped into three categories:
type 1: has a depth of 1-3 mm (26.3% of the population)
type 2: has a depth of 4-7 mm (73.3% of the population)
type 3: has a depth of 8-16 mm (0.5% of the population)
Type 3, or asymmetry of the depth of the olfactory fossa, exposes more of the very thin cribriform plate to potential damage from trauma, tumor erosion, CSF erosion (in benign intracranial hypertension) and local nasal surgery/orbital decompression 2,5.
This, in turn, places the olfactory bulb and anterior ethmoidal artery at risk and predisposes to CSF rhinorrhea.
History and etymology
This classification was described in 1962 1 by Predrag Keros (1933-2018) 3, a Croatian physician and later Professor of Medicine at the University of Zagreb.
References
- 1. Keros P. On the practical value of differences in the level of the lamina cribrosa of the ethmoid. Z Laryngol Rhinol Otol. 1962;41:809-13.
- 2. Gauba V, Saleh G, Dua G, Agarwal S, Ell S, Vize C. Radiological Classification of Anterior Skull Base Anatomy Prior to Performing Medial Orbital Wall Decompression. Orbit. 2006;25(2):93-6. doi:10.1080/01676830600674627 - Pubmed
- 3. Journal of Applied Health Sciences = Časopis Za Primijenjene Zdravstvene Znanosti. 4(1):125-39.
- 4. Almushayti Z, Almutairi A, Almushayti M, Alzeadi H, Alfadhel E, AlSamani A. Evaluation of the Keros Classification of Olfactory Fossa by CT Scan in Qassim Region. Cureus. 2022;14(2):e22378. doi:10.7759/cureus.22378 - Pubmed
- 5. Mahdian M & Karbasi Kheir M. CBCT Assessment of Ethmoid Roof Variations Through Keros, Gera, and TMS Classifications. Int J Otolaryngol. 2022;2022:3708851. doi:10.1155/2022/3708851 - Pubmed
- 6. Abdullah B, Chew S, Aziz M et al. A New Radiological Classification for the Risk Assessment of Anterior Skull Base Injury in Endoscopic Sinus Surgery. Sci Rep. 2020;10(1):4600. doi:10.1038/s41598-020-61610-1 - Pubmed
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