Endoscopic sinus surgery (ESS) is a common procedure; it is indicated for chronic rhinosinusitis which is not controlled by medical management [1, 2], and this is furthermore done in cases of nasal polyposis, mucocele, sellar and parasellar tumours and optic nerve decompression and other intracranial lesions by using extended approaches of the ESS [3, 4].

The chief problems of ESS are ophthalmic damage, meningitis, cerebrospinal fluid leak and intracerebral vessel damage [5,6,7]. The ethmoid bone is the main site of maximum complications of ESS [8,9,10,11].

As stated by previous studies, the lateral lamella of the cribriform plate is the most common site of damage during ESS [12,13,14,15,16]. The delicate area in the skull base is where the anterior ethmoidal artery goes into the cranial cavity [17, 18].

The fovea ethmoidalis is a continuation of the orbital plate of frontal bone and forms the roof of the ethmoid. This forms a boundary between the ethmoidal cells and the anterior cranial fossa [19]. It is connected to the lateral lamella of the cribriform plate medially [10, 20].

The height of lateral lamella of the cribriform plate governs the depth of the olfactory fossa. Based on its depth, Keros categorized the olfactory fossa into three types as follows: Keros type 1 (< 3 mm), type 2 (4–7 mm) and type 3 (8–16 mm). An inconsistent section of the lateral wall of the olfactory fossa will be bare during ESS in the frontoethmoidal region based on the type of Keros. The type 3 Keros is more at risk of injuring the lateral lamella of the cribriform plate during ESS [21, 22].


To assess the anatomical variations of type of ethmoid roof and depth of olfactory fossa as per Keros classification.

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