Axonotmesis of the Sciatic Nerve

Diagnostic and Interventional Imaging (2012) 93, 398—400

LETTER / Neurology

Axonotmesis of the sciatic nerve

a,∗ b c c

M. Ohana , S. Quijano-Roy , F. Colas , C. Lebreton ,

c c

C. Vallée , R.-Y. Carlier

Radiology Department, Nouvel Hôpital Civil, Strasbourg University Hospitals, 1, place de

l’Hôpital, 67000 Strasbourg, France

Paediatrics Department, Raymond-Poincaré Hospital, 104, boulevard Raymond-Poincaré,

92380 Garches, France

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

92380 Garches, France

Case report

KEYWORDS

Peripheral nerve; We report the case of an eight-year old girl who was admitted for aftercare and rehabilita-

MRI; tion one month after a serious head injury that required a four-day stay in intensive care.

Axonotmesis Initial investigations did not show any evidence of post-traumatic injury.

During her admission, she developed signiﬁcant pain in the left buttock radiating to the

lower limb associated with a sensorimotor deﬁcit. These disabling pains persisted at rest.

The clinical examination revealed that the patient had great difﬁculty walking, presenting

a limp, a tender point on palpation of the left buttock radiating to the thigh and the leg

along a posterolateral course, with hyperaesthesia in the whole area. Extension of the

leg and both ﬂexion and extension of the foot were impossible; hip ﬂexion was normal.

Hypoaesthesia was noted on the inside of the left leg and foot. The left patellar and Achilles

reﬂexes were absent. Vital signs were normal.

First-line magnetic resonance imaging (MRI) of the lumbar spine did not reveal any

abnormalities.

An MRI of the pelvis and lower limbs was then carried out and this highlighted involve-

ment of the sciatic nerve along its whole extra-perineal course (Fig. 1a), with an overall

increase in its calibre (Fig. 1b), a clear and homogenous high T2 signal intensity and a loss

of its fascicular structure compared to the contralateral side (Fig. 1c). The nerve remained

uninterrupted along its whole course.

∗

Corresponding author.

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

Axonotmesis of the sciatic nerve 399

Figure 1. MRI of the pelvis and lower limbs: a: coronal STIR; b: axial T1; c: axial T2 SPAIR. Clear and continuous high-signal intensity of

the left sciatic nerve along its extra-perineal course (a), with an increased calibre compared to the contralateral side (b, right arrow). On

T2-weighted SPAIR sequences (c), the normal fascicular appearance visible on the right (small right arrows) is not found on the injured side

(curved arrow).

surrounded by a structure of connective tissue called the

On electroneuromyography, the territory of the left sci-

endoneurium. Several axons group as a nerve fascicle, which

atic nerve showed marked signs of acute denervation: the

is enclosed in a further layer of connective tissue, the per-

tibialis anterior, semimembranosus and semitendinosus mus-

ineurium. A variable number of fascicles (up to a hundred)

cles were affected, showing an increased insertion activity,

are grouped together to form the nerve trunk, encased

positive waves and ﬁbrillations. The tensor fascia latae

by the epineurium. The Seddon classiﬁcation is the sim-

muscle (innervated by the superior gluteal nerve — L5), the

plest scale available, distinguishing three levels of pathology

gluteus maximus muscle (inferior gluteal nerve — S1), the

depending on the depth of the post-traumatic injury:

psoas muscle (femoral nerve — L2/L3) and paravertebral •

neurapraxia: the trauma causes destruction of the myelin

muscles (branches L5/S1) were intact, with no spontaneous

sheath, without affecting the axons or causing rupture of

activity and normal voluntary contractions.

the surrounding connective tissue. This local conduction

The diagnosis of post-traumatic nerve injury also known

blockage resolves fully in less than twelve weeks;

as high-grade axonotmesis of the sciatic nerve, secondary •

axonotmesis: the trauma causes destruction of the

to a trauma located at the notch, as suggested by the imag-

myelin sheath and downstream wallerian degeneration.

ing results was conﬁrmed by the electroneuromyogram and

The encapsulating connective tissue (endoneurium)

the patient’s clinical evolution. Final clinical outcome was

is preserved, thus serving as a guide for proximodistal

slowly favourable over several months.

axonal regrowth. Recovery is slow (1 mm/day) and usually complete;

Discussion •

neurotmesis: there is a full section of the nerve, with

Post-traumatic nerve injuries can be categorised using Sed- disrupted continuity in all the layers and downstream

don’s clinical classiﬁcation [1], based on the histological wallerian degeneration. Surgical intervention to re-

anatomy of the nerve ﬁbre (Fig. 2). The axon is the base establish continuity is required, or nerve regrowth will

unit of a peripheral nerve; it can be myelinated and is end up forming a proximal neuroma.

400 M. Ohana et al.

Figure 2. Schematic anatomy of the peripheral nerve.

The MRI appearance of peripheral nerves is concor- common in animal models (nerve crush in mice) but have

dant with their anatomy [2]. On T1-weighted sequences, rarely been reported in humans.

the nerve appears isointense compared to the muscle,

sometimes demonstrating a peripheral halo of high-

Disclosure of interest

signal intensity corresponding to the epineurium fat. On

T2-weighted sequences, the nerve appears with a moder-

The authors declare that they have no conﬂicts of interest

ately high signal due to endoneurial ﬂuid; high-resolution

concerning this article.

acquisitions can demonstrate its fascicular ultrastruc-

ture.

Under experimental conditions, wallerian degeneration References

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