Keywords
trigeminal neuralgia - anatomy - cadaver - endoscopy
Introduction
Trigeminal neuralgia (TN) is characterized by severe, recurrent facial pain along
one or more of the trigeminal nerve divisions.[1] For patients with severe, medication refractory symptoms, there are several destructive
and nondestructive surgical techniques that are available including microvascular
decompression, stereotactic radiosurgery, and percutaneous rhizotomy.[1]
[2] Fluoroscopic percutaneous radiofrequency rhizotomy (RFR), balloon compression (PBC),
and glycerol rhizotomy (PGR) are simple procedures with excellent success rates up
to 90%[3]
[4]; however, these procedures can pose technical challenges with unsuccessful cannulation
of the foramen reported in 2.7 to 8.0%.[5]
[6] These techniques are usually performed with fluoroscopy to visualize the bony structures
such as the foramen ovale ([Fig. 1]); however, the soft tissue anatomical structures are not visible, and therefore,
the nerves and vessels are always at risk of injury, e.g., the internal carotid artery
and internal jugular vein course posterior to the foramen ovale ([Figs. 2] and [3]). Intraoperative bleeding may be caused by puncture of the internal carotid artery,
internal jugular vein, maxillary artery, middle meningeal artery, or pterygoid venous
plexus.[7] A previous cadaveric study clearly showed puncture of the second part of the maxillary
artery following percutaneous procedures.[8] The branches of the mandibular division of the trigeminal nerve are also near the
needle trajectory ([Fig. 3]). Thus, it impossible to avoid injury of these soft tissue anatomical structures
with blind placement of needles destined for the foramen ovale.
Fig. 1 Skull base of a dry skull noting the trajectory toward the left foramen ovale used
in transfacial approaches.
Fig. 2 (A) Inferolateral view of the right skull base noting the trajectory used for transfacial
approaches to the right foramen ovale. Important regional anatomy includes the internal
carotid artery and internal jugular vein found posterior to the foramen ovale and
V3. (B) Anterior view of the trajectory used for transfacial approaches to the left foramen
ovale. Note V3 exiting the foramen and the more posteriorly located internal carotid
artery and internal jugular vein.
Fig. 3 (A) Cadaveric dissection of the left infratemporal fossa noting V3 exiting the foramen
ovale (dotted curved line) that has been partially opened. A large pterional craniotomy with removal of parts
of the maxilla and mandible has been performed to show the important regional anatomy
including the trigeminal ganglion (TG), V1-V3 branches, buccal nerve (cut) (BN), lingual
nerve (LN), inferior alveolar nerve (IAN), auriculotemporal nerve (ATN), maxillary
artery (MA), medial pterygoid muscle (MP). (B) Cadaveric dissection of the left infratemporal fossa zoomed in compared with Fig.
4 and noting V3 exiting the foramen ovale. Also, note the buccal nerve (BN), lingual
nerve (LN), inferior alveolar nerve (IAN), auriculotemporal nerve (ATN), deep temporal
nerve (DTN), maxillary artery (MA), middle meningeal artery (MMA), and medial pterygoid
muscle (MP).
Over the past decade, minimally invasive endoscopic procedures and approaches have
been used to treat various neurosurgical diseases[9]; however, percutaneous procedures in TN have not yet been supplemented by the endoscopic,
video-assisted techniques that could provide better outcomes with less complications.
As this approach might encounter and potentially injure important anatomical structures,
visualization of structures during advancement of the needle toward the foramen ovale
would be beneficial. Therefore, this study aimed to assess the feasibility of using
endoscopy as an adjunct to percutaneous approaches for TN.
Materials and Methods
We conducted a cadaveric study on latex-injected specimens to assess the utility and
feasibility of the endoscopic-assisted foramen ovale approach. This study comprised
eight cadaveric sides heads that underwent an endoscopically assisted percutaneous
approach using Hakanson's anterior puncture method for targeting the foramen ovale.
The specimens consisted of two males and two females with a mean age at death of 71
years (range 67–80 years) at the time of death.
Surgical Approach
On each side, the conventional Hakanson's anterior puncture method[10] for the entry point of the needle (14-gauge Tuhoy needle) was used. This method
introduces the needle approximately 3 cm lateral to the angle of the mouth where the
line from the medial point of the pupil and the point 2.5 cm anterior to tragus intersected
([Fig. 4]). We then introduced the endoscope (NeuroPEN Neuroendoscope, Medtronic, USA) parallel
to the needle and moved the needle and endoscope as a unit for guidance superiorly
toward the foramen ovale at the skull base. Post procedure, the course of the endoscope
and needle was evaluated for gross injury to regional nerves and blood vessels. Finally,
the endoscope was used to approach the foramen ovale in two dry, adult skulls to visualize
the anatomy of the foramen and surrounding relationships as would be seen on fluoroscopy
during use of such a procedure in patients, that is, without related soft tissues.
Fig. 4 Tuohy needle placement aimed at the left foramen ovale with endoscope inserted alongside
the needle as it is advanced superiorly.
Results
None of the cadavers exhibited evidence of gross disease, previous surgical procedures,
or traumatic lesions to the face or skull base. V3 exiting the foramen ovale ([Fig. 5]) was easily visualized with the endoscope on all sides. While approaching the foramen
ovale, the large distal branches of V3 including the lingual and inferior alveolar
nerves were first identified as they traveled between the medial and lateral pterygoid
muscles. These branches were then traced proximally up to the main V3 trunk deep to
the lateral pterygoid and the needle placed into the foramen ovale. Large arteries
(maxillary artery) and veins (pterygoid venous plexus) were easily visualized and
avoided during the approach to the foramen ovale. No gross injury to any neurovascular
structure along the course of the needle insertion was identified. The anatomy of
an inferior view of the foramen ovale as would be seen on fluoroscopy was easily appreciated
with the endoscope used on dry skulls.
Fig. 5 Anteroinferior view of the left lingual nerve (LN) and inferior alveolar nerve (IAN)
as V3 is approached with the endoscope. Also note the auriculotemporal nerve (ATN)
extending posteriorly from V3.
Discussion
This cadaveric study demonstrated successful cannulation of the foramen ovale on all
sides using an endoscopically assisted technique. With the endoscope, we first encountered
the distal branches of V3 among the pterygoid muscles, and then successfully following
these superiorly to the main trunk of V3 at the foramen ovale. There was no gross
damage to surrounding neurovascular structures following detailed post-endoscopic
dissection. Based on these results, this method could feasibly be used in percutaneous
procedures to access the foramen ovale for patients with TN.
Trigeminal neuralgia (tic douloureux) is clinically characterized by paroxysmal, severe,
and recurrent facial pain along the trigeminal nerve distribution, affecting one or
more branches and causing functional limitation.[1] It is estimated that one in 15,000 to 20,000 individuals suffer from TN; however,
the incidence could be higher owing to frequent misdiagnosis.[11]
Although multiple mechanisms have been proposed, neurovascular compression of the
dorsal root entry zone at the ventral aspect of the pons is the most accepted hypothesis.[1] The exact pathophysiology of TN remains controversial. However, it is thought that
chronic nerve compression results in demyelination at the transition zone between
peripheral and central myelination zones causing progressive axonal degeneration of
myelinated and unmyelinated fibers, with ultrastructural and biochemical changes at
the nerve root and in the trigeminal ganglion.[12]
The diagnosis of TN is primarily clinical; however, most physicians perform advanced
imaging including a brain magnetic resonance imaging (MRI) using diffusion tensor
imaging (DTI) and three-dimensional fast imaging employing steady-state (3D FIESTA)
sequences to rule out mass lesions, central demyelination, other secondary pathological
changes affecting the nerve root, and properly identify and characterize neurovascular
compression (NVC) if present.[13]
[14]
[15]
[16]
There are several destructive and nondestructive surgical techniques for patients
with severe symptom that are poorly controlled with medications.[1]
[2] Microvascular decompression (MVD) is a surgical treatment of choice for TN resistant
to medical management, especially in otherwise healthy young patients with evidence
of NVC on MR or CT imaging, which provides the best results for long-duration pain
freedom.[1]
[17] In contrast, percutaneous procedures and stereotactic radiosurgery are among the
surgical treatments of choice for pain recurrence, poor surgical candidates, multiple
sclerosis cases, and/or in the absence of NVC.[1]
[18]
[19]
Fluoroscopic RFR, PBC, and PGR are simple procedures with excellent success rates
up to 90% complete or satisfactory pain relief[3]
[4]; however, this procedure can pose technical challenges with unsuccessful cannulation,
which is reported in 2.7 to 8.0% of cases.[5]
[6]
Skull base fluoroscopic guidance has its own associated learning curve, and even in
experienced hands, cannulation using Hartel's approach and Hakanson's anterior puncture
has a technical failure rate of 1 to 5%.[20] Moreover, a significant positive correlation has been reported between good cannulation
and success rate with cerebrospinal fluid (CSF) outflow.[4] Given its technical challenge and lack of CSF return in some cases, making the conventional
fluoroscopic confirmation of adequate cannulation less certain, some studies have
proposed salvage procedures using CT- and MRI-guided navigation and frameless navigation
to overcome these challenges for accurate cannulation of the foramen ovale and Meckel's
cave with improving outcomes.[21]
[22]
[23]
Minimally invasive procedures and approaches have been used to treat various neurosurgical
diseases.[9] Over the past decade, endoscopic approaches have gained popularity and have been
used for spinal, transcranial, and skull base approaches.[9]
[24]
[25]
[26] The endoscopic technique in TN has been used alone for MVD or as an adjuvant to
the microscope, which allows better visualization for effective and completed decompression
with improved pain relief and fewer surgical complications and less brain retraction.[1]
[27]
[28]
[29]
[30] However, percutaneous procedures in TN have not yet been supplemented by video-assisted
procedures.
To our knowledge, this is the only cadaveric study to have quantified and assessed
the utility and feasibility of endoscopy-assisted percutaneous procedures in TN.
In this study, we have detailed the application of endoscopy-assisted percutaneous
trigeminal rhizotomy as a salvage approach. We found that this technique allows for
intraoperative confirmation of foramen ovale cannulation. Additionally, such a method
might better appreciate anatomical variations, e.g., bony bars in the region of the
foramen ovale and aid in navigating around such obstacles.
Conclusion
This report details the application of endoscopic video-assisted percutaneous trigeminal
rhizotomy. We found this salvage approach to be feasible. It allows for intraoperative
confirmation of foramen ovale cannulation, anatomical identification of surrounding
structures, and positioning of the needle tip in Meckel's cave under direct visualization.
Such a procedure, after it is confirmed in patients, could offer a new technique for
reducing unsuccessful canalization and could improve outcomes.
