DR NIJALINGAPPA

FELLOW IN RADIOLOGY

TNMC AND NAIR HOSPITAL

MUMBAI

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.

Vascular compression syndrome has been described as a causative etiologyfor 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.

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.

Trigeminal nerve course and branches

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.

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).

In the Meckel cave, the nerve forms a mesh-likeweb that can be visualized only with high-resolutionimaging.

Along the anterior aspect of the cavity, thetrigeminal nerve forms the trigeminal (Gasserian /Semilunar) ganglion before splitting into threesubdivisions.

Imaging pitfall –

Trigeminal ganglion lacks blood-nerve barrier, sonormally enhances in post contrast images.

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.

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.

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 anteroinferiorMeckel cave.

The cerebrospinal fluid within Meckel cave communicates with prepontine cistern through the porus trigeminus.

abrupt unilateral shock like facial pain localized to

the sensory supply areas of the trigeminal nerve

(CNV) lasting seconds to minutes.

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

The most frequent cause of TN is a mechanicalirritation of the nerve caused by neurovascularcontact—the neurovascular compressionsyndrome (NVCS)

It is widely believed that compression atvulnerable sites only—those in the so-called rootentry or exit zone of the nerve—causes NVCS.

Most investigators define the root entry or exitzone as the region extending from the nerve’spoint of entry into or exit from the brainstem tothe point of transition from the central myelin(derived from the oligodendroglia) to theperipheral myelin (derived from Schwann cells)

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.

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.

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.

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)

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

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.

Grooving, distortion, or deviation of the

trigeminal root, which has been reported

to be more specific for idiopathic

trigeminal neuralgia

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

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.

•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 thesuperior cerebellar artery (short arrow) has compressed the REZ

of the right trigeminal nerve (long arrow) at the medial site.

The average diameter of the unaffectedtrigeminal nerve has been estimated ontransverse MR images to be 4 mm, with therange being 2–6 mm .

In the majority of cases, there is atrophy of thenerve tissue which is secondary to chroniccompression of the nerve by aging andtortuous vessels along the course of the nerveafter its point of exit from the brainstem.

Up to 42% of symptomatic nerves have grossatrophy.

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)

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).

Paulo Roberto Lacerda Leal ,et al

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,

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

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.

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.

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.

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).

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.

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).

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.

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.

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

Examples of types of AICA loops and eighth CN-AICA relationships.

Gultekin S et al. AJNR Am J Neuroradiol 2008;29:1746-

1749

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.

Glossopharyngealnerve emerges from thelateral medulla into thelateralcerebellomedullarycistern, above thevagus nerve and at thelevel of the facialnerve.

The vagusnerve comprises tworoots that emergefrom the side of themedulla, from agroove called theposterolateral sulcus.

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.

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.

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.

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

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

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.

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.