Current and Future Imaging of the Peripheral Nervous System

Home , Neurotmesis, Polyneuropathy

Diagnostic and Interventional Imaging (2014) 95, 17—26

REVIEW / Neuroradiology

Current and future imaging of the peripheral nervous system

a,∗ b c d

M. Ohana , T. Moser , A. Moussaouï , S. Kremer ,

e f d

R.Y. Carlier , P. Liverneaux , J.-L. Dietemann

Department of Radiology, Nouveau Civil Hospital — Strasbourg University Hospitals, 1, place

de l’Hôpital, 67000 Strasbourg, France

Department of Radiology, Montreal University Hospitals —Notre-Dame Hospital, 1560

Sherbrooke East, Montreal (Quebec), Canada

Department of Radiology, Sainte-Odile Clinic, 6, rue Simonis, 67100 Strasbourg, France

Department of Radiology II, Hautepierre Hospital — Strasbourg University Hospitals, avenue

Molière, 67098 Strasbourg, France

Department of Radiology, Raymond-Poincaré Hospital, 104, boulevard Raymond-Poincaré,

92380 Garches, France

SOS main, CCOM — Strasbourg University Hospitals, 10, avenue Baumann, 67403 Illkirch,

France

KEYWORDS Abstract Peripheral nervous system (PNS) imaging is usually carried out by ultrasound and MRI.

Peripheral nervous Thanks to its wide availability and excellent spatial resolution, ultrasound is a mature investiga-

system; tion with clearly established indications, particularly in entrapment syndromes and tumors. MRI

Ultrasound; is generally a second-line examination, which provides decisive additional information thanks to

MRI; its excellent contrast resolution and its multiplanar abilities. This review describes the current

Neurography methods for imaging the PNS, concentrating on acquisition techniques, normal results and basic

pathological semiology. Ongoing and future developments are described in order to underline

the forthcoming changes in this very dynamic ﬁeld of musculoskeletal radiology.

The nervous system is divided into the central nervous system (CNS) which consists of

the brain, spinal cord and retina, and the peripheral nervous system (PNS) which is made

up of all of the other nervous structures [1].

The PNS is therefore made up of nerves, ganglions, various receptors and synaptic and

motor nerve endings, which carry CNS commands to the effector organs and return internal

and external sensory informations. Each structure is essential in transmitting the nerve

impulse, but because of its length, speciﬁc histology function and exposure to diseases,

the peripheral nerve remains the main focus of PNS imaging.

∗

Corresponding author.

E-mail address: [email protected] (M. Ohana).

18 M. Ohana et al.

Macrophages then clean up the cell debris and release

A few pathophysiologic concepts

growth factors which stimulate axonal development. Sev-

Histology eral buds therefore develop from the axon stump. One of

these buds becomes predominant and keeps advancing in a

A peripheral nerve is a rope-shaped organ which has a spe- proximal to distal direction, guided and stimulated by the

ciﬁc concentric organization designed to guide, protect and remaining endoneural environment. Nerve regrowth occurs

nourish neuronal ﬁbers within it. The main structure is the at a rate of 1 to 2 mm per day and its effectiveness increases

axon [1] which is a long extension of the neuronal cell body in positive correlation with the closeness of the section mar-

specialized in transporting the nerve impulse. It is constantly gins. Should the nerve margins be too far apart, the axonal

sheathed in a support cell, the Schwann cell, whose special- buds will no longer have a guide and may grow anarchically,

isation differentiates two types of ﬁbers: forming a mass, the amputation neuroma.

•

unmyelinated ﬁbers, surrounded by a single small diam- This clearly deﬁned degeneration followed by axonal

eter layer of Schwann cytoplasm, which conducts slowly regrowth sequence only occurs completely and effectively

and mostly has sensory (pain) and vegetative functions; in clear-cut nerve section or focal nerve compression. This

•

myelinated ﬁbers, around which the Schwann cell wraps can be seen in the experimental setting (by tying off the

in multiple layers to form the myelin sheath. These nerve in the nerve crush model [4]) or clinically in a wound

myelinated ﬁbers vary in diameter, are generally involved from a sharp object such as a blade or a broken piece of

in rapid, responsive conduction and constitute all the glass.

somatic motor ﬁbers and a large proportion of the sensory

ﬁbers.

Classiﬁcation of post-traumatic peripheral

nerve injuries

These myelinated and unmyelinated peripheral nerve

ﬁbers lie in a loose connective tissue called the

Traumatic nerve injuries, however, involve a far greater

endoneurium, made up of ﬁbroblasts, a collagen matrix

spectrum of damage, ranging from simple compression to

and blood capillaries. They group in bundles, each bun-

total destruction with loss of tissue. The more disorganized

dle being demarcated by a solid concentric cell layer, the

the ultrastructure of the nerve has become, the less likely

perineurium. Several fascicles (from a few units to a hun-

nerve regrowth is to occur.

dred) are grouped together to form the actual nerve trunk,

Several nerve damage classiﬁcations have been described

which is separated from the surrounding environment by

to reﬂect this relationship. The most widely used is the Sun-

a dense ﬁbrous connective tissue, the epineurium, within

derland classiﬁcation (1978) inspired by the work of Seddon

which many blood vessels, the vasa nervorum, circulate.

(1943) [5]. It consists of ﬁve stages [6]:

This concentric histology [2] is shown schematically in Fig. 1. •

Sunderland I (neuropraxia according to Seddon): a local

conduction block secondary to focal demyelination,

therefore involving destruction of the myelin sheath but

Wallerian degeneration

with no damage to the axon or rupture of the endoneural

After section or crush, axons forming the peripheral nerves support tissue. Recovery occurs fully within 12 weeks;

•

are able to regenerate slowly [1]. Sunderland II (axonotmesis according to Seddon): this

In the ﬁrst hours after an injury, the axon and the involves a loss of axonal continuity, with complete dis-

Schwann cells forming its myelin sheath begin to disinte- tal Wallerian degeneration. The supporting connective

grate. This starts immediately distal to the site of injury and tissue is preserved and the endoneural tubes guide the

follows a proximal to distal path. This phenomenon, due to proximal to distal axonal regrowth (‘‘Schwann stakes’’).

the post-traumatic interruption of axonal ﬂow, and there- Complete recovery usually occurs but requires several

fore the shortage of the essential substances for the axon months, depending on the distance which has to be ren-

to survive, is known as Wallerian degeneration [3] and lasts ervated;

•

between one and two weeks, depending on the length of the Sunderland III: the damage locally destroys the axon, the

nerve involved. myelin sheath and the endoneural tubes. The perineurium

Figure 1. Schematic anatomy of the peripheral nerve.

Current and future imaging of the peripheral nervous system 19

and epineurium remain intact. Regrowth is variable but

generally incomplete because of incorrect orientation of

the ﬁbers and trapping in the endoneural scar;

•

Sunderland IV: only the epineurium remains intact with

endoneural scarring and loss of endoneural and perineural

continuity. The scarring prevents regrowth of the ﬁbers

and results in the formation of a neuroma;

•

Sunderland V (neurotmesis according to Seddon): the

nerve is totally dislocated, affecting the endoneurium,

epineurium and perineurium. As in stage IV, only surgery

can offer a hope of nerve regrowth.

Muscle denervation

The section of a motor nerve has direct consequences on the

innervated skeletal muscle, the ﬁrst one being paralysis.

Wallerian degeneration ultimately reaches the neu-

romuscular junction, which is thereby destroyed. The

denervated muscle ﬁber will at ﬁrst develop vasogenic

edema [7]. These abnormalities are seen electromyographi-

cally from 48 hours [8], and a typical histological appearance

is seen after 3 weeks [9]. These changes usually reverse

Figure 2. Sixty-one-year-old man. Curvilinear reconstructions of

when the endplate regenerates.

the right sciatic nerve from a lower limb CT angiogram.

If the denervation persists, metabolic changes within

the muscle will progress to muscle ﬁber atrophy and an

Table 1 Advantages and disadvantages of CT scanning

increase in their fat content. Chronic denervation leads to

to examine the peripheral nervous system (PNS).

diffuse fatty inﬁltration of the affected muscles after several months [10].

Advantages Disadvantages

Good spatial resolution Irradiation

Excellent bone contrast Poor contrast

Current PNS imaging methods

Large ﬁeld of view resolution

Volume acquisition with Occasionally requires

PNS imaging relies mostly on ultrasound and MRI: com-

multiplanar iodinated contrast

puted tomography has a more limited input. Conventional

Reconstructions (MPR) injection

radiography has only indirect applications, researching bony

Readily available Generally provides only

causes in entrapment syndromes (fracture, supernumerary

Quickly performed indirect information on

bone, bone callus, etc.) [11,12].

Interventional guiding for PNS disease

diagnostic and therapeutic Computed tomography

procedures

CT is useful in diagnosing intradural, intraforaminal and

extraforaminal spinal nerve compression [13]. It is also

useful in the etiological diagnosis of some entrapment syn- Ultrasound

dromes, particularly if a bone-based, tumoural or vascular

cause is suspected [14]: its good spatial resolution, excellent

The arrival of high frequency probes and reﬁnement in

bone contrast and the ability to perform CT angiography are

electronics have resulted in a clear improvement in the spa-

advantages in this situation.

tial resolution of ultrasound. Peripheral nerves, which are

CT can also be used to diagnose peripheral nerve tumors

generally very superﬁcial, have beneﬁted from these new

[15]: it has good spatial resolution and can easily detect

developments, as already demonstrated in 1987 [19]. Many

a mass [16], although it may be difﬁcult to conﬁrm its

subsequent studies [20—25] have conﬁrmed the beneﬁts of

neural origin. It is also a useful investigation in type 1

the method and its advantages (Table 2).

neuroﬁbromatosis [17], where it provides a precise stag-

Using musculoskeletal presets and high frequency lin-

ing of the neuroﬁbromas, investigating for gastro-intestinal,

ear probes (10 to 17 MHz), the majority of peripheral nerve

pulmonary or urinary compressions and related bone defor-

trunks, i.e. the median, radial, ulnar, sciatic, common ﬁbu-

mities.

lar and tibial nerves, can be examined [22].

Apart from these indications, and although the large

The nerve is identiﬁed and its perineuronal environ-

nerve trunks are often clearly visible on CT [18] (Fig. 2), its

ment studied on axial sections in which the peripheral

contrast resolution is inadequate for detailed examination

nerve appears as an oval structure, consisting of a network

and identiﬁcation of pathological changes in the neuronal

of hypoechogenic fascicles separated by hyperechogenic

microstructure.

septa. In longitudinal sections, it appears as a tube contain-

The advantages and disadvantages of CT are summarized

ing hypoechogenic bands separated by hyperechogenic lines

in Table 1.

(Fig. 3). The hypoechogenic bands correspond to the nerve

20 M. Ohana et al.

relatively homogeneous, with posterior acoustic enhance-

Table 2 Advantages and disadvantages of ultrasound to

ment [15,28]. The proximity of the mass to the nerve is an

examine the peripheral nervous system (PNS).

essential diagnostic feature [29]. Some signs can suggest a

Advantages Disadvantages histological subtype such as a lesion decentered relatively

to the nerve course which is more common in schwannomas.

Excellent spatial resolution Operator dependent

The ultrasound distinction between schwannomas and neu-

No contraindications Relatively long learning

roﬁbromas remains however arbitrary [30] and in any event

Dynamic investigations curve

of limited use in practice.

possible Poor contrast

Ultrasound has two roles in entrapment syndromes:

Investigation of a large resolution •

to look for nerve morphology abnormalities as a result of

part of the nerve path Limitations in some

compression, which may produce two major signs [22]:

Interventional ultrasound deep or difﬁcult to ◦

a segmental change in diameter, usually focal thinning

with diagnostic and access anatomical

at the point of compression and downstream enlarge-

therapeutic procedures areas

ment immediately after the compression; an increase

Readily available

in nerve diameter may also be seen proximal to the

Low cost

compressed area [24]. Some authors propose the mea-

surement of nerve cross-sectional area or the ﬂattening

ratio [25], with cut-offs to distinguish patients from

healthy controls,

◦

a loss of the usual fascicular echostructure, the nerve

becoming hypoechogenic in which nerve fascicles are

difﬁcult to visualize;

•

to identify lesions in the perineuronal environment

responsible for compression: soft tissue tumors, osteoar-

ticular abnormalities such as synovial cysts, tenosyn-

ovitis or supernumerary tendons and vascular abnor-

malities.

In polyneupathy, some studies [31] have shown a signiﬁ-

cant increase in nerve diameter (mostly the median nerve),

particularly in hereditary Charcot-Marie-Tooth neuropathy

[32,33].

Magnetic resonance imaging

At the beginning of the 1990s, Howe & Filler team pro-

posed an examination entirely dedicated to the visualization

of the PNS with suitable sequences optimizing the contrast

between nerves and their environment, called neurography

[34,35]. The use of phased-array coils and a high ﬁeld imager

signiﬁcantly improve the signal to noise ratio and the spa-

tial resolution, allowing the neuronal ultrastructure to be

Figure 3. Twenty-eight-year-old man. Ulnar nerve ultrasound at

examined [36,37].

the wrist in axial and longitudinal sections. 12 Mhz linear probe.

The protocols use [37—40]:

Typical fascicular appearance. •

T1-weighted spin-echo sequences, providing good mor-

phological evaluation and excellent spatial resolution;

•

bundles and the hyperechogenic lines are the epiperineural T2-weighted spin-echo sequences, which have good con-

supporting connective tissue [26]. However, less than 30% trast resolution;

•

of the true number of nerve fascicles are actually seen on these ‘‘simple’’ T2 sequences have been replaced by

ultrasound and this proportion declines with the frequency ‘‘neurography’’ sequences [37,41] which are highly

of the probe used [27]. weighted T2 sequences using long echo times (100 ms)

This characteristic fascicular structure allows peripheral combined with fat signal suppression. Vascular satura-

nerves to be distinguished from tendons, which have a ﬁbril- tion bands are usually added on both sides of the region

lar echostructure. Nerve mobility during movements is of being investigated in order to reduce the vascular inﬂow

low amplitude, unlike the neighboring muscles and tendons. signal. The ﬁeld of view is limited to what is strictly nec-

Doppler studies are usually negative on a normal nerve [24]. essary, with a matrix as large as possible and ﬁne sections

In pathology, ultrasonography performs well in the (2 to 4 mm) in order to maximize the spatial resolution.

diagnosis of neoplastic diseases. These are generally Either spin-echo sequences (SE or TSE) with fat saturation,

benign tumors (neuroﬁbromas and schwannomas) and or Short Tau Inversion Recovery (STIR) sequences which

appear as an oval or fusiform tissular lesion with regular, provide more reliable homogeneous fat suppression are

clearly demarcated outlines. They are hypoechogenic and used;

Current and future imaging of the peripheral nervous system 21

•

T1 weighted sequences after gadolinium injection: these

Table 3 Advantages and disadvantages of MRI to exam-

are occasionally required in tumour or inﬂammatory dis-

ine the peripheral nervous system (PNS). eases.

Advantages Disadvantages

Excellent contrast resolution Contraindications to

The section planes should be adjusted depending on the

Very good spatial MRI

region being examined: an axial plane is essential [40] and

resolution Availability and

occasionally sufﬁcient but is often combined with a perpen-

Three-dimensional planes appointments delays

dicular plane.

No limitation in examining High cost

The advantages and disadvantages of MRI are summarized

deep structures Static investigation,

in Table 3.

Good investigation of occasionally performed

MRI ﬁndings on the peripheral nerve are consistent with

muscle mass (signs of in un-physiological its anatomy [36].

denervation) positions

On T1 weighted sequences, the nerve appears isoin-

Research and development Limited ﬁeld of view

tense with muscles, with a peripheral hyperintense halo,

potential Long acquisition time

representing the epineural fat [38,42]. The isointense

Investigation is less

nerve bundles can be distinguished within the hyperintense

operator dependent

connective epi- and perineural tissue [39] in the major nerve

trunks with high-resolution acquisitions.

On T2 weighted sequences, the nerve is moderately •

increase in diameter, particularly a segmental increase

hyperintense. The fascicles within the large nerve trunks

preceded and followed by a nerve of normal diameter, is

exhibit a more pronounced hyperintensity due to the

also considered pathological;

endoneural ﬂuid [39] (Fig. 4). •

hyperintensity on ‘‘neurography’’ sequences: this is

Non-pathological nerve structures demonstrate no signif-

reported to be a result of a decrease in axonoplasmic ﬂow

icant enhancement after contrast injection (because of the

due to neuronal degeneration and peri- and endoneural

presence of the blood-neuronal barrier).

edema [37,41];

As with ultrasound, pathological features concern the •

a loss of the fascicular structure on the T2 and particularly

morphology and signal of the nerve structure:

• T2FS weighted sequences also indicates disease and is due

ﬂattening of the nerve, particularly in areas liable to be

to the same causes;

compressed, is abnormal. This sign is particularly valu- •

moderate contrast enhancement on T1 weighted

able if it is segmental and associated with an increase in

sequences after gadolinium injection: this reﬂects a

diameter of the upstream nerve segment;

breach of the blood-nerve barrier.

Figure 4. Twenty-eight-year-old man. Sagittal T1 and T2FS MRI sections of the median nerve in the carpal tunnel on a 3T scanner. Note the

peripheral hyperintensity on the T1 weighted sequence, representing the epineural fat, and the fascicular appearance with hyperintensity

of the tubes on the T2FS weighted sequence.

22 M. Ohana et al.

MRI also allows a good appreciation of the overall path

of the nerve: a non-physiological deviation or change in

direction is evidence for compression or a pathological adhe-

sion. It is therefore an excellent investigation to assess

entrapment syndromes [21,43], particularly for recurrences

or failures after surgery [12,44,45].

MRI is also extremely useful for examining the perineural

environment: its excellent contrast resolution and its ability

to carry out multiplanar acquisitions facilitates the diagnosis

of intrinsic [15,28] or extrinsic compressive lesions.

MRI can also be useful for the positive diagnosis of inﬂam-

matory polyneuropathies by demonstrating contrast uptake

and increased diameter of the cauda equina nerve roots

[46,47]. An old study showed that in some cases the diagnosis

was conﬁrmed by MRI ﬁndings despite a negative electroneu-

romyogram [48].

Wallerian degeneration is visible experimentally on MRI

as early as 24 hours after the initial injury [49]. It produces Figure 5. Forty-eight-year-old man, one month after an injury

a clear hyperintense T2 signal [50], with loss of usual fas- causing complete section of the collateral ulnar and radial nerves

cicular structure and an overall increase in nerve diameter. in his left thumb. T2FS weighted axial section. Hyperintensity on the

These abnormalities are due to an increase in water content T2 sequence in the thenar eminence due to acute muscle denerva-

tion.

as a result of intra- and perineural edema, secondary to rup-

ture of the blood-neuronal barrier and inﬂux of phagocyte

cells.

of this technique to the peripheral nerve system [55,56],

It is therefore theoretically possible to distinguish

with acquisition of a T1 weighted and T2 STIR weighted

neuropraxia (no abnormalities on imaging), axonotmesis

three-dimensional sequences.

(Wallerian degeneration without loss of nerve continuity)

They provide high quality isotropic neurography, with

and neurotmesis (Wallerian degeneration with complete loss

the possibility for curvilinear multiplanar reconstructions

of continuity) [51] by MRI. In practice, the distinction is not

and post-treatment such as MIP or image fusion, which are

that clear and is primarily based on clinical and electromyo-

particularly useful in examining complex anatomical struc-

graphic ﬁndings.

tures like the brachial plexus. This sequence can already

Finally, muscle denervation can be seen on MRI and

be used in everyday practice without changing equip-

is a valuable indirect evidence of damage to the nerve ment.

innervating the muscle area in question [52]. As a gen-

eral rule, the nervous lesion is located more proximally

than the muscle abnormality [39]. Muscle denervation is

seen on MRI as two chronologically consecutive appearances [10,37,38]:

•

initially the muscle remains normal in size and mor-

phology, with clear global hyperintensity on T2 weighted

sequences (Fig. 5). The edema is visible early, experi-

mentally from 48 hours [53], and persists throughout the

acute and subacute phase of denervation, usually for less

than 10 weeks and very rarely for more than 6 months.

The intensity of the increased T2 signal is reported to be

proportional to the severity of the nerve damage [54]. Sig-

niﬁcant muscle enhancement is seen at this phase after

gadolinium injection;

•

secondarily, loss of muscle volume associated with a

hyperintense T1 signal (Fig. 6) is seen: this is the fatty

amyotrophic stage characterizing the chronic phase of

denervation, which occurs in the months following the

initial lesion and persists if renervation does not occur

[10].

Developments and future prospects

Figure 6. Eighty-ﬁve-year-old woman, who had a whole body

Volume neurography MRI to investigate camptocormia. T1 weighted axial slices. Stage

IV chronic fatty amyotrophy in the anterior tibial and left soleus

3D volume acquisitions have been achievable on MRI for muscles, and stage II-III in the right soleus muscle, due to sciatic

many years and several authors have reported application sequelae.

Current and future imaging of the peripheral nervous system 23

Microneurography appears to be an objective and early means of measuring

sensory neuronal damage following peripheral nerve lesion.

This technique [57] optimizes the spatial resolution of neu- In contrast, an increase in the size of the spinal gan-

rography images, using very high magnetic ﬁelds, extremely glion has been found in chronic inﬂammatory demyelinating

powerful gradients and speciﬁc coils. Using a 9.4 Teslas polyneuropathy. This increase can also be observed in inher-

scanner and gradients of 400 mT/m, images of anatomical ited neuropathies or those secondary to lymphoma, and is

parts can be obtained with a spatial resolution of 30 ␮m. believed to be due to inﬂammatory and edematous changes

These acquisitions of stunning histological precision show us with demyelination and remyelination cycles. Measurement

what could be done with neurography when the MRI method of cervical and lumbar spinal ganglia with coronal STIR

is pushed to its limits. acquisitions can then be used to diagnose affected subjects

This can be compared to very high frequency ultrasound, [65]. The hypertrophy also correlates positively with the

which uses dedicated probes to increase the spatial reso- electrophysiological abnormalities.

lution, at the expense of the investigation depth. 55 Mhz

microprobes are used in ex vivo animal research and provide

MRI spectroscopy

a theoretical spatial resolution of 30 ␮m [58].

This technique is used to identify and quantify several

Dedicated contrast media metabolites thanks to their resonance frequency differ-

ences. Its major limitation is its poor contrast resolution

Tw o molecules may be useful in PNS MRI investigation: (routinely 7 to 10 mm) which is not really compatible

•

Superparamagnetic MR contrast agents (SPIO - Endorem with examination of peripheral nerves. In an old publica-

or Resovist) and Ultrasmall Superparamagnetic contrast tion, Baldassarri [66] astutely circumvented the problem

agents (USPIO - Sinerem), containing iron oxide parti- by examining muscle metabolism during nerve regeneration

cles, which identify the inﬂammatory response thanks with P spectroscopy to quantify high-energy metabolites

to their afﬁnity for the macrophage system. Accumula- and estimate intramuscular pH. Muscle tissue alkalinization

tion of these molecules produces a hypointense signal was found during the denervation phase. These abnormal-

on gradient-echo acquisitions through a paramagnetic ities disappeared following complete regeneration of the

effect. Bendszus [59] was able to visualize macrophage motor nerve, allowing it to be monitored indirectly.

inﬂux from day 1 to day 8 in Wallerian degeneration and A recent study [67] on animal models used F MRI spec-

Stoll [60] demonstrated PNS inflammation with contrast troscopy and perfluorocarbon labeling. Perflurocarbon has

uptake beginning before clinical symptoms and resolving afﬁnity for the macrophage system and its binding is there-

at the peak of disease in an animal model of the Guillain- fore an indirect marker of neuronal inﬂammation. This

Barré syndrome. The problem with these applications is technique does not yet, however, seem applicable to human

that the products are not available commercially; beings.

•

gadoﬂuorine belongs to the family of micellar contrast

media, which is still experimental, and binds to the

Diffusion, diffusion tensor imaging and

areas of nervous demyelination, producing a hypointense

tractography

T1 signal until remyelination is complete. It appears to

be both highly sensitive and speciﬁc, and can detect

The description of peripheral nervous system appear-

focal demyelination lesions. This may be useful in

ance on diffusion-weighted sequences is relatively recent.

post-treatment follow-up of autoimmune and inherited

Takahara [68,69] introduced the concept of diffusion-

demyelinating diseases [61,62].

weighted MR neurography (DW-MRN), based on diffusion-

weighted sequences with baseline signal suppression. These

Contrast-enhanced ultrasound sequences optimally showed the path of nerve trunks, par-

ticularly on MIP reconstructions. The technique has been

An animal study has shown that contrast-enhanced ultra- described in several anatomical sites [70], and even success-

sound is feasible in peripheral nerve imaging [63], enabling fully in wholebody acquisition [71], which could enable the

quantitative measures of PNS perfusion. Pathology applica- entire PNS to be examined in a single investigation. Its spa-

tions have been suggested, particularly in traumatology to tial and contrast resolution, however, are still inadequate.

monitor grafted nerve injuries. Most authors who study diffusion actually concentrate

on diffusion tensor imaging and tractography, an MRI tech-

nique used to produce an in vivo reconstruction of the

Spinal ganglion morphometry

path of neuronal ﬁbers based on their anisotropism. The

ﬁrst tractography reconstruction of a peripheral nerve dates

The spinal ganglion is formed by the cell bodies of the pri-

back to 2004, when Skorpil [72] used a CNS tractography

mary sensory neurons. Its morphology can therefore change

protocol on the sciatic nerve and demonstrated that the

in peripheral nervous diseases and indirectly reﬂect these.

technique could be used on three healthy individuals. Many

In an experimental study on mice using a high ﬁeld (7 Tes-

authors have since conﬁrmed the validity of the technique

las) imager, West showed that 3D MRI measurement of spinal

and have looked for applications in pathology, particularly

ganglion volume correlated well with histological measure-

to diagnose carpal tunnel syndrome [73,74]. The tractogra-

ments, which themselves were directly proportional to the

phy sequences can be optimized [75] in order to obtain high

number of neuronal cell bodies [64]. A reduction in spinal

quality reconstructions for the large nerve trunks (Fig. 7).

ganglion volume therefore reﬂects a loss of neurons and

24 M. Ohana et al.

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