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ORIGINAL ARTICLE
Anatomic characteristics of the dural sheath of the trigeminal nerve
Yilei Li, PhD,1 Xi-an Zhang, MD,2* Songtao Qi, MD2
1
Department of Pharmacology, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, People’s Republic of China, 2Department of Neurosurgery,
Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong, People’s Republic of China.
Accepted 17 December 2014
Published online 20 June 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/hed.23968
ABSTRACT: Background. The purpose of this study was to clarify the
anatomic characteristics and discuss the clinical implications of the dural
sheath of the trigeminal nerve, especially its compartmentalization.
Methods. The dural sheath of the trigeminal nerve was microsurgically
dissected in 8 formalin-fixed adult cadaver heads (16 sides).
Results. The dural sheath of the trigeminal nerve is meningeal dura in
origin and composed of Meckel’s cave and the peripheral sheaths. The
peripheral sheath is a direct continuation of Meckel’s cave, but separated from the latter by a cribriform area from where the nerve rootlets
INTRODUCTION
The parasellar region has long been a challenging surgical
target because of its intrinsic anatomic complexity. First
described by Dolenc et al,1–3 the transcavernous approach
and its variations have become key skull base techniques
for treating various vascular and neoplastic cavernous
sinus lesions, as well as for surgical management of complex basilar tip aneurysms. More recently, the endoscopic
endonasal approach has been proposed as a minimally
invasive surgical technique for the removal of parasellar
lesions.4,5 However, both of these approaches to the parasellar region have the potential to be a somewhat bloody
procedure or cause severe complications if the surgeon is
not familiar with the complicated anatomy in this dangerous region.
The construction of the lateral wall of the cavernous
sinus is one of the most important anatomic issues and is
crucial to the success of either open or endonasal parasellar surgery. A few authors have extensively studied the
arrangement of the dural layers composing the lateral
wall of the cavernous sinus and their relationships with
the dural sheaths of cranial nerves.6–12 Up to now, however, no definitive detailed anatomic study of the interior
of the dural sheath has been published. The purpose of
*Corresponding author: X. Zhang, Department of Neurosurgery, Nanfang
Hospital, Southern Medical University, 1838 Guangzhou Dadao Bei Street,
Guangzhou, 510515, People’s Republic of China.
E-mail: [email protected]
Contract grant sponsor: This work was supported by The National Natural
Science Foundation of China (No. 81102475) and by the High-level Matching
fund from Nanfang Hospital, Southern Medical University, China (81102475).
pass through. Within the peripheral sheaths, there are a few septa,
which are frequently interrupted by connections among nerve rootlets.
Conclusion. The cribriform area of Meckel’s cave, which divides the
dural sheath of the trigeminal nerve into 2 distinct compartments, may
C 2015
play an important role in tumor growth and surgical planning. V
Wiley Periodicals, Inc. Head Neck 38: E185–E188, 2016
KEY WORDS: anatomy, trigeminal nerve, Meckel’s cave, cavernous
sinus, dura matter
this anatomic study was to clarify the anatomic characteristics and discuss the clinical implications of the dural
sheath of the trigeminal nerve, which is the most complex
one among the cranial nerves traversing the cavernous
sinus.
MATERIALS AND METHODS
A total of 8 preserved adult human heads were microsurgically dissected. In 6 of the 8 heads, the calvaria and the
brain were removed. Then, the target area (12 sides) was
studied from outside toward the center. The remaining 2
heads were bisected sagittally in the midline and the bone
related to the cavernous sinus and the pituitary fossa was
removed. The target area (4 sides) was dissected medially
to laterally. A Leica M651 surgical microscope (Leica Co,
Heerbrugg, Switzerland) was used for microsurgical dissections, with a Canon EOS 600D (Canon, Tokyo, Japan)
attached for photographic documentation.
RESULTS
The dural sheath of the trigeminal nerve looks like a 3fingered glove and has 2 parts: Meckel’s cave housing
the nerve root and the gasserian ganglion, and the peripheral sheaths enveloping the 3 major divisions of the trigeminal nerve (Figure 1). Meckel’s cave is formed by
evagination of the posterior fossa dura into the middle
fossa. Only the meningeal layer contributes to its formation. Therefore, Meckel’s cave is located between the
endosteal layer covering the middle fossa and the meningeal layer facing the underneath of the temporal lobe
(Figure 2A and 2B). Meckel’s cave has a smooth inner
surface and no major separation.
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dural sheaths of the trigeminal nerve’s 3 major divisions
are all meningeal dura in origin and accompany the corresponding nerves to leave the middle cranial fossa and
fuse with the epineurium extracranially.
DISCUSSION
Dural architecture of the dural sheath
of the trigeminal nerve
FIGURE 1. Schematic drawing showing the architecture of the
dural sheath of the trigeminal nerve. Note that the cribriform area
separates Meckel’s cave from the peripheral sheaths and the
anastomoses among the intrasheath septa are common. Also
note that only the motor root does not pass through the cribriform
area, but rather enters a separate sheath in the inferior wall of
Meckel’s cave. M, motor root of the trigeminal nerve; MC, Meckel’s cave; V1, ophthalmic dural sheath; V2, maxillary dural
sheath; V3, mandibular dural heath.
Along the periphery of Meckel’s cave, the 3 peripheral
sheath are not communicated with Meckel’s cave by a
sizable opening. Rather, there are a few small openings at
the junction area between the superior and inferior walls
of the Meckel’s cave, which we called the “cribriform
area” in this study (Figure 1). It is from these small apertures in the cribriform area, the preganglionic nerve rootlets exit the peripheral sheaths to enter Meckel’s cave
(Figure 2C). However, the motor root enters a separate
sheath in the inferior wall of Meckel’s cave and then
joins laterally with the peripheral dural sheath of the mandibular nerve (Figures 1 and 2D).
As compared with that of Meckel’s cave, the most distinguishing feature of the peripheral sheaths is the abundant septa within the dural sheath (Figures 1 and 2E).
However, these septa usually do not form closed tubular
channels. Divergence and coalesce of preganglionic nerve
rootlets are frequent findings, thus also form a plexiform
appearance like that of the postganglionic nerve rootlets
within Meckel’s cave (Figure 2E).
Although different in appearance, these 3 peripheral
sheaths are a direct continuation of the meningeal dura
forming the Meckel’s cave, because they can be easily
peeled off from both the superficial layer of the lateral
CS wall and the endosteal layer lining the middle cranial
fossa and the bony foramens (Figure 2F). Therefore, the
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The dura mater of the brain is comprised of 2 layers:
an outer or endosteal layer and an inner or meningeal
layer. The endosteal layer is continuous with the pericranium through the cranial foramina and with the orbital
periosteum through the superior orbital fissure. The
meningeal layer is reflected on the surface of the cranial
nerves to form dural sheaths as they pass out through the
cranial foramina or superior orbital fissure, and then these
sheaths usually are in continuity with the epineurium
extracranially.11,13 At the parasellar region, the juxtaposition of the meningeal dural sheaths of the cranial nerves
traversing the lateral wall of the cavernous sinus, with a
frequently incomplete reticular membrane extending
between the nerve sheaths, forms the so-called inner layer
of the lateral cavernous sinus wall.12 Our findings are in
consistent with the classic description.
Contrary to the description given by most authors, Janjua et al7 held that there is also an intermediate fibrous
layer between the superficial and deep layers of the lateral cavernous sinus wall. We cannot agree with these
authors and found only 1 layer superficial to Meckel’s
cave and the 3 peripheral sheaths. In our dissection, we
found that the superficial layer of the lateral cavernous
sinus wall is thinner anteriorly and inferiorly, but thicker
posteriorly and superiorly. As we know, within the dura
the collagen fibers are densely packed in fascicles, which
are arranged in the lamina. The fascicles run in different
directions in adjacent laminae. This may lead to dissection artifact, as mentioned by Goel14 that the outer dural
layer of the lateral cavernous sinus wall “often by sharp
dissection can be separated into two or more layers.”
The most important finding in our study is the cribriform area of Meckel’s cave, which divides the dural
sheath of the trigeminal nerve into 2 distinct compartments and may play an important role in tumor growth
and surgical planning. To the best of our knowledge, this
has not been described before. The reason that this important anatomic issue has been overlooked in previous studies is unclear, probably because of natural adhesion
between the gasserian ganglion and peripheral part of
Meckel’s cave.15 The role of the intrasheath septa in partitioning the peripheral sheath is not as important as that
of the cribriform area in separating the peripheral sheaths
from Meckel’s cave. This is because these intrasheath
septa are frequently interrupted by connections among
nerve rootlets and thus do not form closed spaces.
Striking similarity between dural sheaths
of the trigeminal and olfactory nerves
Although the dural sheath of each cranial nerve has its
own peculiarity, our observations suggest that there are
striking similarities between the trigeminal and olfactory
TRIGEMINAL
DURAL SHEATH
FIGURE 2. Anatomic characteristics of the dural sheath of the trigeminal nerve. (A) The superior wall of Meckel’s cave can be easily separated
from the superficial layer of the lateral wall of the cavernous sinus (left side viewed medially). (B) The endosteal layer beneath and the endosteal
structures in relation to the inferior wall of Meckel’s cave (left side viewed posteromedially). (C) The cribriform area (green arrow for porus with
nerve rootlet removed and blue arrows for porus with nerve rootlet passing through) between Meckel’s cave and peripheral dural sheath of maxillary nerve after partial removal of the gasserian ganglion (right side viewed laterally). (D) The motor root (black arrows) leaves Meckel’s cave via a
separate sheath in the inferior wall (right side viewed laterally). (E) The septa within the peripheral sheath and connections among the nerve rootlets (right side viewed laterally). (F) The continuity between Meckel’s cave and the peripheral dural sheaths (left side viewed medially). Note that in
panel F, the peripheral dural sheath can be easily separated from the endosteal layer of middle fossa dura, the latter of which is continuous with
the pericranium (black arrowheads) extracranially. APC, anterior petroclinoid ligament; ICA, internal carotid artery; II, optic nerve within dural
sheath; III, oculomotor nerve within dural sheath; IV, trochlear nerve within dural sheath; MC, Meckel’s cave; PL, petrolingual ligament; PP, petrosphenoid ligament; PPC, posterior petroclinoid ligament; V, trigeminal nerve; V1, ophthalmic nerve and/or corresponding peripheral dural sheath;
V2, maxillary nerve and/or corresponding peripheral dural sheath; V3, mandibular nerve and/or corresponding peripheral dural heath; VI, abducens
nerve within dural sheath.
nerves with respect to the dural organization of their
transcranial segments. The nerve fibers in both nerves
collect into branches, each of which has its dural sheath.16
The nerve branches traverse the foramina of a cribriform
structure, the cribriform area of Meckel’s cave form the
trigeminal and ethmoid cribriform plate for the olfactory
nerve, and finally end in the gasserian ganglion or the
olfactory bulb for synapsing.
Clinical implications of the compartmentalization
of the transcranial trigeminal nerve
The trigeminal neuroma can arise from any part of the
trigeminal nerve between the root and the distal extracranial branches. In the literature, several classifications of
trigeminal neuroma have been proposed and are oriented
either to the cranial fossa or to the part of the dural
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sheath involved.2,17–19 Accepting the fact that, at least in
the early stage of tumor growth, the continuity of the anatomic membrane surrounding the tumor is always preserved in benign neuroma, it is understandable that the
latter type of classification, as first suggested by Dolenc,2
is better in formulating the surgical strategy, especially
for small to medium-sized middle fossa tumor. The exact
site of origin of the trigeminal neuroma in relationship to
the cribriform area of Meckel’s cave dictates the spread
of tumor. Therefore, the concept of the cribriform area of
Meckel’s cave is practically important in differentiating
the peripheral branch type (I) and Meckel’s cave type (II)
in Dolenc’s classification. However, the role of the cribriform area of Meckel’s cave in limiting tumor spread
should not be overemphasized, because this porous membrane cannot be as durable as the intact dura layer. As
the tumor grows in size, the adjoining foramina in the cribriform area become more and more expanded, allowing
the tumor to spread into the adjacent compartment. This
is why in trigeminal neuroma tumor involvement of both
the peripheral sheath and Meckel’s cave are more common than true cavernous sinus invasion or temporal dura
breach.2,20–22
A tendency of spread through perineural spaces is a
common characteristic of some malignant tumors of the
head and neck origin, including but not limited to, sarcomas, squamous cell carcinomas, and adenoid cystic carcinomas.23–26 The trigeminal nerve involvement at the floor
of the middle cranial fossa is not uncommon. Under these
circumstances, the involved trigeminal nerve needs to be
removed to obtain a clear margin, which is usually
accomplished by endoscopic endonasal approach or anterior craniofacial approach currently.5,24 A major concern
is whether there is risk of cerebrospinal fluid leak when
cutting the trigeminal nerve endonasally. Because of the
presence of the cribriform area at the junction between
Meckel’s cave and the peripheral sheath, the risk of postoperative cerebrospinal fluid leak is minimal if the cut is
only needed to be distal to the cribriform area, especially
when the stump is coagulated to plug up the cribriform
area.
As with other anatomic studies, the obvious limitation
of the present study was the inability to ascertain the
actual role of the cribriform area of Meckel’s cave in
influencing the growth pattern of trigeminal neuroma,
which warrants further clinical study. Another limitation
of this study was the lack of information about the trigeminal dural sheath from the endoscopic endonasal perspective because of unavailability of endoscopy during
this study.
CONCLUSIONS
Our results show that there are points of similarity
between the trigeminal nerve and olfactory nerve with
respect to the dural organization of their transcranial segments. The presence of the cribriform area, rather than
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tubular communication between Meckel’s cave and the
peripheral sheath, may play an important role in tumor
extension. It is also a surgically important landmark for
surgical planning and evaluating the risk of postoperative
cerebrospinal fluid leak.
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