Key-words:
Cyberknife - trigeminal neuralgia - vertebrobasilar dolichoectasia
Introduction
Trigeminal neuralgia is a chronic clinical condition secondary to multiple causes.
Trigeminal neuralgia caused by vertebrobasilar dolichoectasia (VBD) is an extremely
rare condition. The incidence is 0.05%.[[1]] Primarily, VBD is a vascular disorder characterized by a dilated, elongated, and
tortuous vertebrobasilar system. It is characterized by paroxysmal hemifacial pain.
We are describing a patient who developed trigeminal neuralgia secondary to VBD and
successfully treated with Cyberknife stereotactic radiosurgery.
Case Report
A 66-year-old male presented to our outpatient department with the history of severe
left-sided facial pain lancinating in type and associated with difficulty in chewing
food on the left side. Pain distributed along the maxillary and mandibular components
of the trigeminal nerve. He was diagnosed 7 years back clinically with trigeminal
neuralgia and was started on tablet carbamazepine 100 mg thrice daily and the dose
was increased to 200 mg thrice daily. He had no pain relief with medical management.
Pain assessment was done using the Barrow Neurological Institute Pain Intensity Score.
The initial assessment was a score of V (severe pain or no pain relief) before treatment.
A preliminary magnetic resonance imaging (MRI) of the brain with contrast was done
which showed tortuous dilated right vertebral artery coursing in the prepontine cistern,
extending to the left cerebellopontine angle, abutting and displacing the left trigeminal
nerve (cisternal) to the lateral side. Mild altered morphology with flattening of
the surface left trigeminal nerve was noted [[Figure 1]].
Figure 1: Coronal section of the magnetic resonance imaging of the brain showing the dilated
vertebral artery due to vertebrobasilar dolichoectasia
He was planned for Cyberknife stereotactic radiosurgery with single-fraction treatment
using MRI and computed tomography (CT)-based planning. At the region of interest MRI
Images with Constructive Interference in Steady state sequence of 0.6 mm slice thickness
and CT scan with 1.25 mm slice thickness were acquired and fused using Cyberknife
Data Management System (CDMS) [[Figure 2]]. Contouring was done using both CT and MRI scans [[Figure 3]]. Brainstem and vertebral arteries were organs at risk. Multiplan system version
4.6.1 was used for planning with sequential optimization. The dose to the target was
66 Gy in single fraction prescribed to the 83% isodose line [[Figure 4]].
Figure 2: The above image is the fusion of the planning computed tomography scan and constructive
interference in the steady-state sequence of magnetic resonance imaging, the red line
is the target area that is the proximal nerve root entry zone
Figure 3: Axial section magnetic resonance imaging of the brain (constructive interference
in steady-state series) showing the course of the trigeminal nerve
Figure 4: Three-dimensional beam planning with Cyberknife radiosurgery for trigeminal neuralgia
(TN)
The treatment was delivered with Cyberknife radiosurgery system which consists of
6MV, X band linear accelerator mounted on fully articulated robotic arm. It has precision
of 0.3 mm with six degrees of freedom. Real-time imaging of bony anatomy with two
orthogonally positioned X-ray detectors was done using 6D-skull tracking on CyberKnife
VSI Radiosurgery System (Accuray Inc., Sunnyvale, CA, USA) 6D skull tracking mode
was used to identify the skull and track the skull motion in six degrees of freedom
based on the fixed relationship between the target volume and the skeletal features
of the skull to correct the intrafraction movement errors.
After premedications, single-fraction radiation was delivered. Immediately after treatment,
the patient noticed pain relief with improvement in chewing food. The Barrow Neurological
Institute Pain Intensity Score after treatment was I (no pain, no medications). Even
though the patient had complete pain relief, empirically tablet carbamazepine was
continued with tapering doses and stopped after 1 month. Follow-up was done at 3,
6, 12, and 18 months, respectively; he developed facial numbness posttreatment at
the end of 6 months which was mild and not bothering (Barrow Neurological Institute
Facial Numbness Scale).
Discussion
The term dolichoectasia means distension and elongation. The most common localization
of dolichoectasia is the vertebrobasilar system in the brain.[[2]] The course of the Basilar Artery (BA) lies in the midline or paramedian but medial
to the margin of the sphenoid clivus or dorsum sellae in 98% of the people. In the
interpeduncular fossa, BA divides into both posterior cerebral arteries at the level
of the superior aspect of dorsum sellae. The proposed mechanism for trigeminal neuralgia
is vascular compression at a specific portion of the cisternal segment of the nerve
known as the root entry zone (REZ). REZ is prone to continuous, pulsatile pressure
resulting in “short circuit” of impulses and focal demyelination resulting in pain.
Trigeminal neuralgia is diagnosed clinically and VBD as etiology is confirmed with
imaging. MRI with preferably CISS is useful in identifying the nerves. CISS sequence
produces high-resolution isotropic images using strong T2-weighted three-dimensional
gradient echo technique. CISS sequence is useful to delineate cranial nerves, as it
provides good contrast between cerebrospinal fluid and cranial nerves.
The nerves appear dark gray in CISS sequence. Fast Imaging Employing Steady-state
Acquisition (FIESTA) sequence is also used for better nerve delineation.
The most explored treatment for trigeminal neuralgia secondary to VBD is a surgical
intervention in the form of microvascular decompression. The second-most common treatment
option is the Gamma knife radio surgery (GKRS). Although both surgery- and Gamma knife-based
treatments have resulted in good outcomes in terms of pain relief both being invasive
techniques, require general anesthesia and have potential risks such as hearing loss,
double vision, facial weakness, and stroke as post treatment complications,[[3]] whereas GKRS has unexpected headaches, edema, severe facial pain, and syncopal
episodes after treatment.[[4]] Hence, both techniques require hospitalization to monitor postoperative complications.
Cyberknife radiosurgery (CKRS) is a linac-based robotic stereotactic radiosurgery,
a new option for trigeminal neuralgia treatment, producing good pain relief and can
be used as a definite treatment modality for medically refractory cases. In comparison
to GKRS, CKRS being a frameless noninvasive technique makes it patient-friendly with
no requirement for anesthesia. Gamma knife with a mounted frame needs imaging, planning,
and treatment on the same day which is cumbersome compared to Cyberknife and offers
flexibility in imaging and planning days before the treatment at the patient's comfort.
GKRS can approach the lesion from 190 positions only, whereas CKRS has 1300 positions
to approach the lesion virtually from any angle with pinpoint precision to submillimeter
accuracy. CKRS has real-time tracking of the lesion that can handle body and organ
movement, whereas GKRS has no real-time update; it utilizes static images that are
taken before treatment to fix the location of the lesion. CKRS thus aids in delivering
high dose of radiation to the target volume of the nerve to produce ablation with
accurate precision, eliminating the ability of the nerve to malfunction and cause
pain. Due to the nerve root compression by VBD, the resulting treatment volume is
more, favoring the use of CKRS. It is effective and safe as first line of treatment
with no major adverse toxicities and improved dose homogeneity.[[5]]
In our patient, CKRS was done and the patient experienced immediate pain relief with
no postprocedure complications. Patient is pain free with no requirement of adjuvant
pain medication after two years of Cyberkinfe Stereotactic Radiosurgery.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form, the patient has given his consent for his images and other clinical information
to be reported in the journal. The patient understands that name and initials will
not be published and due efforts will be made to conceal identity, but anonymity cannot
be guaranteed.
