The oculomotor nerve: anatomic relationship with the floor of the third ventricle.
OBJECTIVE
Endoscopic third ventriculostomy (ETV) has become first-line treatment for obstructive hydrocephalus. Many complications have been described, but the literature about oculomotor palsy after ETV is scarce. Therefore we undertook an anatomical study of the relationship of the oculomotor nerve to the floor of the third ventricle.


METHODS
Distances and angles between the third nerve and the bottom of the third ventricle were studied both in two cadaver heads and in high-definition CISS images in 16 MRI scans. The angles of the trajectories putting the nerve at risk or not were compared. Finally, in a retrospective analysis of intraoperative images the appearance of the membranous portion of the floor was defined and if visible, the distance of the third nerve to the midline was estimated by comparing with the 8-mm balloon catheter.


RESULTS
The course of the third nerve is approximately 8 mm laterally and approximately 17 mm caudally distant from the midpoint of the floor of the third ventricle. The angle of the trajectory to damage the third nerve is at least 12° greater than any safe angle of ETV trajectory through a normal burr hole.


CONCLUSIONS
The third nerve is not always visible during ETV procedures, but the angular and linear measurements imply that the risk to damage the nerve should be relatively small. Confirmation of these data in hydrocephalic patients with distorted anatomy is needed.
Department of Neurosurgery, University Hospital Gasthuisberg, Herestraat 49, B-3000, Leuven, Belgium. eveleen.buelens@uzleuven.be
Eveleen
E
Buelens
Guido
G
Wilms
Johannes
J
van Loon
Frank
F
van Calenbergh
D006801:Humans; D044583:Neuroendoscopy / Q000379:methods; D009802:Oculomotor Nerve / Q000033:anatomy & histology* / Q000473:pathology / Q000601:surgery; D012189:Retrospective Studies; D020542:Third Ventricle / Q000033:anatomy & histology* / Q000473:pathology / Q000601:surgery*; D014696:Ventriculostomy / Q000379:methods
J Neurosurg. 2009 May;110(5):858-60
19012481
Neurol India. 2007 Oct-Dec;55(4):355-62
18040108
Surg Neurol. 1994 Dec;42(6):505-16
7825106
Neurosurgery. 2010 Mar;66(3):593-601; discussion 601
20173555
Neurosurg Rev. 2005 Jan;28(1):1-34; discussion 35-8
15570445
J AAPOS. 2007 Apr;11(2):195-6
17280854
J Neurosurg. 2008 Nov;109(5):931-8
18976087
Childs Nerv Syst. 2008 Aug;24(8):943-8
18317779
Minim Invasive Neurosurg. 2000 Dec;43(4):187-9
11270828
Childs Nerv Syst. 2004 Nov;20(11-12):868-77
15197569
J Neurosurg. 2009 May;110(5):852-7
18976061
Childs Nerv Syst. 2004 Nov;20(11-12):878-83
15185113
J Neurosurg. 2006 Sep;105(3 Suppl):187-93
16970231
Neurosurgery. 1997 Dec;41(6):1400-3; discussion 1403-4
9402593
Br J Ophthalmol. 1996 Feb;80(2):177-81
8814752
Childs Nerv Syst. 2009 Mar;25(3):293-9
18802708
Minim Invasive Neurosurg. 1994 Sep;37(1):28-36
7804855
Childs Nerv Syst. 2006 May;22(5):506-13
16404640
Childs Nerv Syst. 2007 Jun;23(6):633-44
17447074
Childs Nerv Syst. 2010 May;26(5):689-96
20012060
Neurosurg Focus. 2005 Dec 15;19(6):E11
16398476
J Neurosurg. 2002 Jun;96(6):1032-40
12066903
Surg Neurol. 2008 Jan;69(1):5-15
18054606
Childs Nerv Syst. 2003 Jun;19(5-6):325-31
12750936
Neurosurgery. 2001 Dec;49(6):1461-4; discussion 1464-5
11859828