Js. Driben et al., THE RELIABILITY OF COMPUTERIZED TOMOGRAPHIC DETECTION OF THE ONODI (SPHENOETHMOID) CELL, American journal of rhinology, 12(2), 1998, pp. 105-111
Optic nerve injury is a devastating potential complication of endoscop
ic sinus surgery. Anatomic variations of the posterior ethmoid sinus a
re certainly contributing factors. In the most well described posterio
r ethmoid anatomical variant, the sphenoethmoid or Onodi cell, the opt
ic nerve is placed at risk during sinus surgery. Improving preoperativ
e and intraoperative identification of the sphenoethmoid (Onodi) cell
could decrease the risk of optic nerve injury. The purpose of this inv
estigation was to assess the reliability of computerized tomography (C
T) in detecting the sphe noethmoid (Onodi) cell, and further our under
standing of this clinically relevant anatomic variant. A total of 41 s
inonasal complexes from 21 human adult cadaveric heads were studied wi
th a standard coronal and axial plane CT, and subsequent endoscopic di
ssection. The prevalence of the sphenoethmoid (Onodi) cell was determi
ned by CT and endoscopic dissection, as were other anatomic characteri
stics of the posterior ethmoid anatomy. In our study, CT identified a
sphenoethmoid (Onodi) cell in 3/41 (7%) of the sphenoethmoid complexes
. However, anatomic dissection identified a sphenoethmoid (Onodi) cell
in 16/41 (39%) complexes. Coronal orientation of the anterior sphenoi
d wall was never associated with a sphenoethmoid (Onodi) cell. Convers
ely, oblique or horizontal orientations were present in all cases of s
phenoethmoid (Onodi) cells. Current CT scanning protocols for the para
nasal sinuses did not reliably detect the Onodi cell. Endoscopic disse
ction indicates that the sphenoethmoid (Onodi) cell is a more frequent
anatomic variant than previously appreciated. Awareness of anterior s
phenoid wall orientation may assist surgeons in identifying the Onodi
cell, thereby reducing the risk of optic nerve trauma.