- Neurovascular compression syndrome (NVCS) refers to nerve compression by aberrant or tortuous blood vessels, which can cause cranial nerve dysfunction including trigeminal neuralgia. - Trigeminal neuralgia is characterized by abrupt, unilateral facial pain and is most often caused by neurovascular compression of the trigeminal nerve at the root entry/exit zone from the brainstem. - MRI with techniques like CISS and MRA-TOF are effective in evaluating neurovascular relationships and compressions, aiding surgical planning for microvascular decompression to treat refractory trigeminal neuralgia.

1. DR NIJALINGAPPA
FELLOW IN RADIOLOGY
TNMC AND NAIR HOSPITAL
MUMBAI

2.  Neurovascular compression syndrome
(NVCS) refers to a group of disorders in
which an aberrant or tortuous vessel
causes nerve compression with
subsequent hyperexcitation and
neuropathy.

3.  Vascular compression syndrome has
been described as a causative etiology
for cranial nerves III, V, VII, VIII, and IX.
 Controversy exists, however, because of
the normal intimate apposition of nerves
and vasculature around the brainstem
and the frequency with which it is seen in
asymptomatic patients.

4.  largest (thickest) cranial nerve
 The roots emerge from the lateral mid-pons and travel
anteriorly through the pre-pontine cistern.
 Enters middle cranial fossa by passing beneath
tentorium at the apex of the petrous temporal bone
& passes through an opening in the dura called the
porus trigeminus to enter the Meckel’s (trigeminal)
cave.

5. Trigeminal nerve course and branches

6.  Meckel (trigeminal) cave is a CSF-containing pouch
in the middle cranial fossa which is continuous with
the pre-pontine sub-archnoid space.
 Pia covers the CN 5 in Meckel’s cave.
 Because the trigeminal nerve is large and its course
proceeds straight forward from the lateral pons, it is
easy to recognize on most MR images.

7. Trigeminal nerve.
FIESTA MR image shows the sensory (arrowhead) and motor (large
arrow) roots of the trigeminal nerve where they cross the prepontine
cistern and enter the Meckel cave (small arrows).

8.  In the Meckel cave, the nerve forms a mesh-like
web that can be visualized only with high-resolution
imaging.
 Along the anterior aspect of the cavity, the
trigeminal nerve forms the trigeminal (Gasserian /
Semilunar) ganglion before splitting into three
subdivisions.
Imaging pitfall –
 Trigeminal ganglion lacks blood-nerve barrier, so
normally enhances in post contrast images.

9.  The ophthalmic (V1) and maxillary (V2) divisions of
the nerve move medially into the cavernous sinus
and exit the skull through the superior orbital fissure
and foramen rotundum, respectively.
 The mandibular division (V3), which includes the
motor branches, exits the skull inferiorly through the
foramen ovale.

10. Trigeminal nerve.
FIESTA image at the level of the Meckel cave shows the complex web of
trigeminal nerve branches (arrows), which coalesce anteriorly to form the
Gasserian ganglion.

12.  Sagittal T2 MR along line of proximal trigeminal nerve shows the
preganglionic segment between the root entry zone in the
lateral pons and the trigeminal ganglion in the anteroinferior
Meckel cave.
 The cerebrospinal fluid within Meckel cave communicates with
prepontine cistern through the porus trigeminus.

13.  abrupt unilateral shock like facial pain localized to
the sensory supply areas of the trigeminal nerve
(CNV) lasting seconds to minutes.

14.  Slight female predominance
› Female 5.9 per 100,000
› Male 3.4 per 100,000
› More than 70% of patients with TN are over
50 years of age at the time onset
 Right side affected slightly more often
 Occasional familial occurrences
 Slightly elevated risk associated with HTN
and multiple sclerosis

15.  The most frequent cause of TN is a mechanical
irritation of the nerve caused by neurovascular
contact—the neurovascular compression
syndrome (NVCS)
 It is widely believed that compression at
vulnerable sites only—those in the so-called root
entry or exit zone of the nerve—causes NVCS.
 Most investigators define the root entry or exit
zone as the region extending from the nerve’s
point of entry into or exit from the brainstem to
the point of transition from the central myelin
(derived from the oligodendroglia) to the
peripheral myelin (derived from Schwann cells)

18.  Demyelination of the sensory fibers of
the CNV due to neurovascular
compression at the root entry or exit
zone is widely regarded as the
underlying pathomechanism
 others being multiple sclerosis /
neoplasms / other space occupying
lesions in the vicinity.

19. Anterior inferior cerebellar artery, a branch
of the same, vertebral artery, superior
cerebellar arteries are usually responsible
for this syndrome.
Commonest area of the
contact is
root entry zone
of preganglionic segment
of the trigeminal nerve.

20.  The reference-standard treatment for
refractive TN caused by NVCS is
microvascular decompression.
 Preoperatively, high-spatial-resolution
magnetic resonance (MR) imaging is
performed to detect the neurovascular
contact and exclude other causes of TN.

21.  MRI along with MRA is considered as an
ideal modality for delineation of the
vessels.
 MR constructive interference in steady
state (CISS) 3D and
 arterial magnetic resonance
angiography time of flight 3D(MRA TOF)

22.  While interpreting the imaging data, one
has to take into account that a
neurovascular contact can also be
present in the form of an anatomic
variant in healthy subjects or on the
unaffected side in patients with TN

23.  The following MRI classification system for
neurovascular compression has been
proposed to aid in surgical planning.
 - Type I: Point compression where a limited
segment of the nerve is in contact with the
vessel.
 - Type II: Longitudinal compression in which
the nerve and vessel traverse parallel to each
other.
 - Type III: A vascular loop encircling the nerve.
 - Type IV: The nerve contour is deformed
and/or thinned.

24.  Grooving, distortion, or deviation of the
trigeminal root, which has been reported
to be more specific for idiopathic
trigeminal neuralgia

25.  In E Lang et al, study ,,
 Vessel–TREZ contact was categorised as
‘‘true positive’’ if a contact between an
artery or a vein and the TREZ was
observed on the symptomatic side.
 Vessel–TREZ contact was categorised as
‘‘true negative’’ if no contact was
observed between an artery or a vein
and the TREZ on the asymptomatic side

27.  Axial (a) fast imaging employing steady-state image and (b) contrast-enhanced
MR angiographic maximum intensity projection of prepontine
fossa in 43-year-old woman show TN involving second branch of CNV.
Another, less obvious example of neurovascular conflict is shown in right CNV
(short arrow). Arterial loop of superior cerebellar artery (long arrow) crosses
right CNV in middle of cisternal course. Neurovascular conflict was confirmed
with surgery. Basilar artery (*) is seen in a.

28. •Images in a 63-year-old man with trigeminal neuralgia, with
NVC caused by the superior cerebellar artery.
•Two adjacent transverse 3D CISS MR images show that the
superior cerebellar artery (short arrow) has compressed the REZ
of the right trigeminal nerve (long arrow) at the medial site.

29.  The average diameter of the unaffected
trigeminal nerve has been estimated on
transverse MR images to be 4 mm, with the
range being 2–6 mm .
 In the majority of cases, there is atrophy of the
nerve tissue which is secondary to chronic
compression of the nerve by aging and
tortuous vessels along the course of the nerve
after its point of exit from the brainstem.
 Up to 42% of symptomatic nerves have gross
atrophy.

30. Trigeminal neuralgia.
Male patient with left facial pain. Axial FIESTA image (A) and sagittal
reconstruction (B) show that the root entry zone of the left trigeminal
nerve is thinned and displaced by an adjacent vessel (thick white
arrow points to the nerve and thin white arrow points to the vessel)

36. Juergen Lutz et al
FA was significantly lower (P = .004) on the
trigeminal neuralgia-affected side
(mean FA, 0.203) than on the
contralateral side (mean FA, 0.239).

37.  Paulo Roberto Lacerda Leal ,et al

38. C. Herweh,et al
 Reversibility of abnormally low FA values
was demonstrated in one patient
successfully treated with microvascular
decompression.
 controls did not show a difference
between both sides,

39. These findings indicate that diffusion-tensor
imaging FA measurement enables in
vivo visualization of the microstructural
changes of the CNV in these patients
Degeneration of white matter tracts
results in a reduction in FA due to a loss of
the directionality of diffusion and
An increase in ADC that are due to
diffusivity being averaged in all spatial
directions as a result of the loss of myelin
and axonal membranes

40.  Trigeminal tractography accurately
detected the radiosurgical target.
 Radiosurgery resulted in 47% drop in FA
values at the target with no significant
change in FA outside the target,
demonstrating highly focal changes
after treatment.

42. Tractography outlines detailed FA changes in the trigeminal nerve after GKRS treatment.
Panels A–D depict the trigeminal nerve tracts pre and post-treatment for
subjects S1(A,B) and S2 (C,D).
The area between the yellow and blue arrows delineates the cisternal
segment, with the yellow arrow being proximal to the brainstem and the blue
arrow distal. The red arrow denotes the target area, which corresponds to the
region where the greatest change in FA was observed. In S1, FA change affects
primarily the outlying fibers of the nerve, while for S2, FA changes are seen in the
inferior portion of the cisternal segment of the trigeminal nerve.

43.  Tractography was more sensitive
than conventional gadolinium-enhanced
post-treatment MR,
since FA changes were detected
regardless of trigeminal nerve
enhancement.
 In subjects with long term follow-up,
recovery of FA/RD correlated with pain
recurrence.

44. Figure 5. Tractography can detect changes in the trigeminal nerve in the absence of post-treatment
gadolinium enhancement: Panels A to E delineate FA changes seen after treatment.
Subject S2 did not show post-treatment MR gadolinium enhancement.
Panel A shows location of radiosurgical target during treatment planning.
Panels B, C depict post-treatment MR and lack of gadolinium-enhancement
(yellow arrowhead). Reconstructed trigeminal tracts are
shown in panel D (pre-treatment) and E (post-treatment), with clear FA
changes in the target area (blue arrowhead).

46.  The facial and vestibulocochlear nerves have similar
cisternal and canalicular courses .
 They both emerge from the lateral aspect of the
lower border of the pons and traverse the
cerebellopontine angle cistern at an oblique angle.
 There, they may be in close proximity to the anterior
inferior cerebellar artery.

47. FIESTA image shows the parallel courses of the facial (black arrowheads)
and superior vestibular (white arrowheads) nerves as they cross the
cerebellopontine angle to enter the internal auditory canal through the
porus acusticus (double arrow).

48. Facial & vestibulocochlear nerves
Facial nerve is anterior & superior to vestibulocochlear nerve within CPA& lAC.
The anteroinferior cerebellar artery loop is a constant fixture in the normal
anatomy of the CPA & lAC area.

49.  Vestibulocochlear NVCS is symptomatic
vascular compression of cranial nerve
VIII.
 Clinical symptoms are often non-specific
including tinnitus, vertigo, and
sensineural hearing loss.
 In decreasing order of frequency, vessels
indicated in NVCS include the anterior
inferior cerebellar artery, posterior inferior
cerebellar artery, and vertebral artery.

50.  type I, lying only in the CPA but not
entering the internal auditory canal
(IAC);
 type II, entering but not extending >50%
of the length of the IAC and
 type III, extending >50% of the IAC

51. Examples of types of AICA loops and eighth CN-AICA relationships.
Axial 3D-FIESTA MR images through the eighth CN show the following: AICA loop
within the IAC (arrow) but not >50% of its depth (Type II) (A); vascular loop
extending into >50% of the IAC (arrow) (Type III) (B); and contact of AICA (arrow)
with the eighth CN, not resulting (C) and resulting (D) in angulation on the eighth
CN (arrow) in the CPA.
Gultekin S et al. AJNR Am J Neuroradiol 2008;29:1746-
1749

52. Glossopharyngeal
nerve emerges from the
lateral medulla into the
lateral
cerebellomedullary
cistern, above the
vagus nerve and at the
level of the facial
nerve.
The vagus
nerve comprises two
roots that emerge
from the side of the
medulla, from a
groove called the
posterolateral sulcus.

53. The glossopharyngeal nerve (CN9), vagus nerve (CNl0) and bulbar accessory
nerve (CNll) all exit the medulla laterally
CN9 is the most cephalad of these. With routine MR imaging it is not possible to see
these three cranial nerves individually.
In the upper medulla the vagus nerve is well seen leaving the brainstem via the
postolivary sulcus. The glossopharyngeal nerve is seen more laterally as it has
already exited the brainstem above the vagus nerve.

54. Coronal oblique SSFP MR image through the cerebellopontine angle shows
the glossopharyngeal nerve (arrow) just beneath the flocculus (f) of the
cerebellum. The two roots of the vagus nerve (arrowheads) are visible in
the same plane, and the superior and inferior vestibular nerves can be
seen above the flocculus.

55.  Glossopharyngeal neuralgia, or
vagoglossopharyngeal neuralgia, is a
cranial nerve hyperactivity pain
syndrome leading to severe, transient,
sharp pain in the ear, base of the
tongue, tonsillar fossa, or beneath the
angle of the jaw corresponding to the
distributions of the auricular and
pharyngeal branches of cranial nerves IX
and X.

56. The presence of neurovascular contact on either side of
the brain stem was evaluated by using the following
criteria:
 Upper and lower borders of the root-entry zone were
determined by uppermost and lowest fibers of the
IX/X nerve bundle entering the medulla.
 The anterior border of the root-entry zone was
defined as the transition of the olivary convexity to
the concavity of the retro-olivary sulcus,
 and the posterolateral border was located at the
junction of parenchymal brain tissue to individual
nerve fibers

59.  most common offending vessel has been
reported to be the
 posterior inferior cerebellar artery (PICA),
 followed by the vertebral artery,
 the anterior inferior cerebellar artery (AICA),
 and other vessels or combinations of vessels

60. Axial CISS (A) and axial fast imaging
with steady-state precession
source images (B) are shown.
The left IX/X nerve bundle is clearly
visible (large white arrowhead on left
side, A).
Left vertebral artery is marked by black
arrow (A), and
anterior border of retro-olivary sulcus is
marked by white arrow (B).
Left descending posterior inferior
cerebellar artery (PICA)impinges
on the retroolivary sulcus, as
indicated by small black (A) and white
(B)arrowheads.

61. Axial CISS, axial fast
imaging with steady-state
precession source
images, and 3D MIP.
there is dominating left
vertebral artery with sharp
angle at level of
pontomedullary junction
(white arrow, C).
Left vertebral artery
shows brain stem contact
within left retro-olivary
sulcus (black arrow A;
white arrow, B).
Thin white arrow in panel
A indicates nerve bundle.