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Dorello Canal Revisited: An Observation that Potentially Explains the Frequency ofAbducens Nerve Injury After Head InjuryR. Shane Tubbs1, Virginia Radcliff1, Mohammadali M. Shoja2, Robert P. Naftel1, Martin M. Mortazavi1,

nna Zurada3, Marios Loukas4, Aaron A. Cohen Gadol5

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INTRODUCTION

The abducens nerve travels a long intracra-nial course, and as a result it is commonlyinjured after head trauma. The abducensnerve can be divided into five segments:three are intracranial (cisternal, gulfar, andcavernous) and two are orbital (fissural andintraconal) (5).

Along its midway course, the abducensnerve travels in Dorello canal, which hascontroversy in the literature regarding itsboundaries. Dorello (4) and Gruber (7)

escribed the canal as lying between thepex of the petrous bone and the petros-henoidal ligament (Gruber ligament)Figure 1). Dolenc (3) described the canals beginning from the entrance of the ab-ucens nerve at the dura covering the cli-us to the cavernous sinus. Umansky et al.

Key words� Abducens nerve� Anatomy� Cranial nerve� Injury� Neurosurgery� Skull base

Abbreviations and AcronymsPVC: Petrovenous gulf

From the1Section

of Pediatric Neurosurgery, Children’s Hospital, Birmingham,Alabama, USA; 2Neuroscience Research Center, TabrizUniversity of Medical Sciences, Tabriz, Iran; 3Departmentf Anatomy, Medical Faculty, University of Varmia andasuria, Olsztyn, Poland; 4Department of Anatomical

Sciences, St. George’s University, Grenada, West Indies;and 5Goodman Campbell Brain and Spine, Department of

eurological Surgery, Indiana University, Indianapolis,ndiana, USA

o whom correspondence should be addressed:aron A. Cohen-Gadol, M.D., M.Sc.

E-mail: acohenmd@gmail.com]

itation: World Neurosurg. (2012) 77, 1:119-121.OI: 10.1016/j.wneu.2011.03.046

ournal homepage: www.WORLDNEUROSURGERY.org

vailable online: www.sciencedirect.com

878-8750/$ - see front matter © 2012 Elsevier Inc.ll rights reserved.

15) described the posteromedial wall

WORLD NEUROSURGERY 77 [1]: 119-121

s consisting of Gruber ligament, yetestrieux et al. (2) used this ligament as

he roof of the canal.Besides the abducens nerve, and depend-

� OBJECTIVE: The abducens nerve issome investigators have attributed tpresent study aimed to elucidate aphenomenon.

� METHODS: Twelve fresh adult caanal using standard microsurgical tec

o the nerve at its entrance into this caigament to observe for movement.

RESULTS: In all specimens, a seconfound within Dorello canal that exclusstructure rigidly fixated the abducens nnot allowing any movement. Transectnerve, but after release of the inner tu

� CONCLUSIONS: Rigid tethering ofwithin Dorello canal affords this nervebrainstem. We hypothesize that this finof abducens nerve injury after head tr

Figure 1. Schematic drawing of the abducensnerve as it travels through Dorello canal. Onthe left side, the nerve enters the dura(beginning of canal) and travels anteriorlytoward the cavernous sinus (end of thecanal) by entering inferior to Gruber ligament,

oseen on the right side of this image.

, JANUARY 2012 ww

ng on the definition used, the dorsal men-ngeal artery and inferior petrosal sinusravel in Dorello canal. As an example ofow various definitions of this canal canffect what contents are included within itsonfines, Umansky et al. (15) did not in-lude the inferior petrosal sinus within thispace.

Because the abducens nerve may becomerapped within Dorello canal (10) and isommonly injured after head injury, theresent study aimed to further elucidate itsrrangement in this region.

ATERIALS AND METHODS

or the present study we chose to defineorello canal as beginning at the dural en-

rance of the abducens nerve (i.e., postcis-ernal or gulfar segment) to its entrancento the cavernous sinus (Figure 1). Twelveresh adult cadavers (24 sides), aged 47– 81ears at death (mean 75 years) and latex in-ected, underwent microsurgical dissection

uently injured after head trauma andto its long intracranial course. Theditional mechanism to explain this

rs underwent dissection of Dorelloues. In addition, traction was applied

before and after transection of Gruber

y tunnel (i.e., tube within a tube) wasy contained the abducens nerve. This

as it traversed Dorello canal, therebyf Gruber ligament did not detach thethe nerve was easily mobilized.

abducens nerve with a second tubebility for movement with motion of theis a main factor in the high incidence

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PEER-REVIEW REPORTS

R. SHANE TUBBS ET AL. DORELLO CANAL

specimens were male and five specimenswere female. An oscillating bone saw wasused to remove the calvaria and then thesupratentorial brain was removed, takingcare not to disrupt any infratentorial struc-tures. Under direct vision, motion of theabducens nerve with manipulation (e.g.,

Figure 2. Cadaveric dissection notiis displaced medially on the clivussuperolaterally in the forceps) ovedepicting the venous sinuses of tinstrument introduced into the tubensheathed as it travels through Dthe meningohypophyseal trunk brartery (ICA) and the cut stump ofthe hooked instrument. DMA, dorpetrosal sinus.

Figure 3. Additional dissection of sportion of the abducens nerve frobranch of the dorsal meningeal arand IT more anteriorly. For additio

segment of the internal carotid artery a

120 www.SCIENCEDIRECT.com

osterior, lateral, inferior displacement) ofhe intact brainstem was performed observ-ng for any movement within Dorello canalefore and after transection of Gruber liga-ent. Next, using a surgical microscope

Zeiss; Germany), dissection of the en-rance of the abducens nerve into Dorello

right abducens nerve (VI), whichdura mater (see retracted

ello canal has been removedgion. Note the inner tube (hookedwhich the abducens nerve is

canal. Also, note the branches ofof the cavernous internal carotidigeminal nerve seen to the right ofeningeal artery; IPS, inferior

en in Figure 2 with removal of ainner tube (IT). Also note a lateral

rossing over the abducens nerveference, note the cavernous

wnd the inferior petrosal sinus.

WORLD NEUROSURGE

anal was performed. The meningeal layerf dura mater covering the dorsal clivus waspened anteriorly to the cavernous sinus,nd observations were made of relation-hips of the abducens nerve in this region.gain, movement of the brainstem was per-

ormed and observations made of the abdu-ens nerve after sequential transection ofhe overlying dura and inner meningealube.

ESULTS

o specimen was found to have intracranialathology in the region dissected. In allpecimens, a secondary tunnel (i.e., tubeithin a tube) was found within Dorello ca-al that exclusively contained the abducenserve (Figures 2– 4). This structure rigidlyxated the abducens nerve as it traversedorello canal, thereby not allowing move-ent. Transection of Gruber ligament or

verlying clival dura did nothing to detachhe nerve, but after the opening of the innerube, the nerve was easily mobilized withinorello canal. The basilar venous plexus

nd inferior petrosal sinuses were all exter-al to the inner meningeal tube, as was theorsal meningeal artery and its branches.ne right-sided specimen was found toave two separate dorsal meningealranches with the more lateral branch ac-ompanying the abducens nerve withinorello canal, but again, external to the in-er dural tube. Each inner tube withinorello canal intimately surrounded the ab-ucens nerve throughout the entire canalut did not compress the nerve. These inter-al tubes maintained the abducens nerve

Figure 4. After the liberation of the abducensnerve from the inner tube and an instrumentplaced between the tube and the base of theclivus.

ng the. Ther Dorhis ree) inorello

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pecimm thetery cnal re

ithin the medial aspect of Dorello canal,

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R. SHANE TUBBS ET AL. DORELLO CANAL

compartmentalizing it from the more later-ally located inferior petrosal sinus.

DISCUSSION

Cranial nerve entrapment neuropathiesmay be due to edematous pressure, venouscongestion, arterial compression that mayrespond to microvascular decompression,lymphatic stasis at extracranial exit sites,bony impingement, membranous tension,or ligamentous pull (10).

Ono et al. (11) mentioned briefly that thepetroclival segment of the abducens nervewas covered by an envelope composed of anarachnoid cell layer. Destrieux et al. (2) ap-preciated this arrangement but observed itinconstantly. Tsitsopoulos et al. (14) foundsuch an envelope in all of their specimensand commented that such an envelope iso-lated the abducens nerve from the inferiorpetrosal sinus within Dorello canal, and ourfindings concur with this. Destrieux et al.(2) defined the “petrovenous gulf” (PVC) asa venous space bordered by endotheliumand continuous with the cavernous, basilar,and inferior petrosal sinuses. Gruber liga-ment has been regarded by some investiga-tors as dividing the PVC into superior andinferior compartments with the abducensnerve, generally, traveling through the infe-rior compartment, where it was fixed to thesurrounding dura mater. We found an innermeningeal tube surrounding the abducensnerve within Dorello canal in all specimens.This morphology separated the nervousfrom venous structures within Dorello ca-nal. Such anatomy is reminiscent of the re-lationship seen in the jugular foramen witha medial pars nervosa and a lateral pars ve-nosum. In cadavers, Ozveren et al. (12)found an arachnoid membrane on the cli-vus that extended within the dural sleevesurrounding the abducens nerve as far asthe petrous apex. The average length of thedural sleeve, described by them, was 9.5mm and the average width was 1.5 mm atthe apex, where the nerve entered the cav-ernous sinus. They (12) found that the sub-arachnoid space inside the dural sleeve ofthe abducens nerve can be defined by usingthin-slice magnetic resonance imagingscans and that enlargement of the duralsleeve at the petroclival region may coexistwith abducens nerve palsy.

A dolichoectatic vertebral artery (6, 9)

WORLD NEUROSURGERY 77 [1]: 119-121

nd anterior inferior cerebellar artery (8)ave been implicated in isolated abducenserve palsies, which may be transient. Linnt al. (8) have suggested a neurovascularompression syndrome involving the abdu-ens nerve. Similarly, De Ridder andenovsky (1) noted intermittent abducens

erve palsy from a dolichoectatic basilar ar-ery that was successfully treated with mi-rovascular decompression. Sandvand et al.13) reported an adult with right-sided in-ermittent abducens nerve palsy due to vas-ular compression of the abducens nerve atts root exit zone by the anterior inferiorerebellar artery. In each of these cases,ethering of the abducens nerve as it enters aeparate tunnel within Dorello canal, mayontribute to this nerve’s sensitivity becausehere is no “give” from mass effect such asrom an ectatic vascular structure.

Based on our findings, abducens nerveompression would not be relieved by sim-ly opening of Dorello canal. In addition,

he inner meningeal tube needs to bepened to decompress the nerve. Manipula-

ion of the abducens nerve near the PVC, asescribed by Destrieux et al. (2), would ne-essitate opening of the inner meningealube.

ONCLUSIONS

obility of the abducens nerve withinorello canal is strictly limited due to the

nner meningeal tube surrounding thiserve. This finding may elucidate the mech-nism for the frequency of abducens nervealsy after head trauma. In addition, such

nformation may assist neurosurgeons whoperate in or near the cavernous sinus ororello canal.

REFERENCES

1. De Ridder D, Menovsky T: Neurovascular compres-sion of the abducent nerve causing abducent palsytreated by microvascular decompression. Case re-port. J Neurosurg 107:1231-1234, 2007.

2. Destrieux C, Velut S, Kakou MK, Lefrancq T, Ar-beille B, Santini JJ: A new concept in Dorello’s canalmicroanatomy: the petroclival venous confluence. JNeurosurg 87:67-72, 1997.

3. Dolenc VV: Anatomy and Surgery of the CavernousSinus. New York: Springer-Verlag; 1989, 68-87.

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4. Dorello P: Considerazioni sopra la causa dellaparalisi transitoria dell’ abducent nelle flogosi dell’orecchio medio. In: Ferreri G, ed. Atti della ClinicaOto-Rion-Laringoiatrica. Roma: Tipografia delCampidoglio; 1905;209-217.

5. Iaconetta G, Fusco M, Cavallo LM, Cappabianca P,Samii M, Tschabitscher M: The abducens nerve: mi-croanatomic and endoscopic study. Neurosurgery61:7-14, 2007.

6. Giray S, Pelit A, Kizilklic O, Karatas M: Isolatedabducens nerve palsy caused by contralateral verte-bral artery dolichoectasia. Neurol India 53:246-247,2005.

7. Gruber W: Beitrage zur Anatomie des Keilbeins undSchlafenbeins. In: Richter HE, Winter A, eds.Schmidt’s Jahrbucher der In-Und Auslandischen.Gesammten Medicin, II, Anatomie und Physiolo-gie. Leipzig: Verlag von Otto Wigard; 1859:40.

8. Linn J, Schwarz F, Reinisch V, Straube A: Ophthal-moplegic migraine with paresis of the sixth nerve: aneurovascular compression syndrome? Cephalalgia28:667-670, 2008.

9. Lin JY, Lin SY, Wu JI, Wang IH: Optic neuropathyand sixth cranial nerve palsy caused by compressionfrom a dolichoectatic basilar artery. J Neurooph-thalmol 26:190-191, 2006.

0. Magoun HI: Entrapment neuropathy of the centralnervous system. Part II. Cranial nerves I-IV, VI-VII,XII. J Am Osteopath Assoc 67:779-787, 1968.

1. Ono K, Arai H, Endo T, Tsunoda A, Sato K, Sakai T,Makita J: Detailed MR imaging anatomy of the abdu-cent nerve: evagination of CSF into Dorello canal.AJNR Am J Neuroradiol 25:623-626, 2004.

2. Ozveren MF, Erol FS, Alkan A, Kocak A, Onal C,Türe U: Microanatomical architecture of Dorello’scanal and its clinical implications. Neurosurgery 60:ONS1-7, 2007.

3. Sandvand KA, Ringstad G, Kerty E: Periodic abdu-cens nerve palsy in adults caused by neurovascularcompression. J Neurol Neurosurg Psychiatry 79:100-102, 2008.

4. Tsitsopoulos PD, Tsonidis CA, Petsas GP, PantelisNH, Ndungu Njau S, Anagnostopoulos IV: Micro-surgical study of the Dorello’s canal. Skull Base Sur-gery 6:181-185, 1996.

5. Umansky F, Elidan J, Valarezo A: Dorello’s canal: amicroanatomic study. J Neurosurg 75:294-298,1991.

onflict of interest statement: The authors declare that therticle content was composed in the absence of anyommercial or financial relationships that could beonstrued as a potential conflict of interest.

eceived January 10, 2011; accepted March 30, 2011

itation: World Neurosurg. (2012) 77, 1:119-121.OI: 10.1016/j.wneu.2011.03.046

ournal homepage: www.WORLDNEUROSURGERY.org

vailable online: www.sciencedirect.com

878-8750/$ - see front matter © 2012 Elsevier Inc.ll rights reserved.

w.WORLDNEUROSURGERY.org 121