MR imaging of the cauda equina in hereditary motor sensory neuropathies: correlations with sural nerve biopsy

Abstract

Background and purpose: Although spinal root abnormalities are known to occur, spinal MR examination is seldom performed in hereditary motor and sensory neuropathies (HMSN). The following work was undertaken to assess the MR imaging spectrum of lumbosacral spinal nerve root abnormalities and determine whether intradural nerve root involvement could be related to any biopsy feature.

Methods: Ten consecutive patients (eight male, two female; age range, 28-65 yrs) with Charcot-Marie-Tooth (CMT) (type I = 5, type II = 2) and Déjèrine-Sottas disease (DSD) (n = 3) underwent a contrast-enhanced lumbosacral MR examination. Sural nerve biopsy was performed in all patients. Atypical clinical features were present in two patients. The MR scans of each patient were reviewed for possible causes of myeloradiculopathy, spinal nerve root and ganglia dimensions, signal change, and abnormal enhancement.

Results: In the seven patients with CMT, abnormal MR findings were intradural nerve root hypertrophy (n = 2), signal abnormalities (n = 2), and enhancement (n = 3). Two of three patients with DSD had the abnormal MR finding of intradural nerve root enhancement. In both patients with atypical clinical features, MR imaging showed nerve root hypertrophy and enhancement. Both findings were related to an increased number of onion bulbs at sural nerve biopsy. Inflammatory infiltrates were not observed in any patients.

Conclusion: In patients with HMSN enhancement of intradural spinal nerve roots, whether or not associated with marked thickening, may be found on lumbosacral MR examinations. Spinal nerve root thickening may be responsible for atypical symptoms, and its visibility on MR images represents a useful adjunct to diagnosis. Lumbosacral spinal nerve root abnormalities were related to an extremely high number of onion bulbs (indicating active demyelination) at sural nerve biopsy. Nerve root enhancement does not seem to be related to inflammatory infiltrates.

fig 1.

A–E, MR images of the lumbosacral spine in a patient with CMT I and atypical clinical features (case 3). Marked thickening of spinal nerve roots, completely filling the spinal canal, is seen on the sagittal (A) and axial (B) FSE T2-weighted (4000/120 [TR/TE]) images. Enhancement of hypertrophic spinal nerve roots and ganglia (arrows) is depicted in the postcontrast SE T1-weighted (TR/TE) sagittal (C) and axial (D) images. A coronal SPIR (E) postcontrast SE T1-weighted scan better depicts spinal ganglia hypertrophy and enhancement by supppressing signal from the paravertebral and foraminal fat.

fig 2.

A–D, MR images of the lumbosacral spine in a patient with the congenital hypomyelinating form of DSD (case 8). Marked diffuse enhancement of the cauda equina nerve roots in the absence of root enlargement is seen on pre- (A) and postcontrast (B) SE T1-weighted (500/15) sagittal images. Fat-suppressed (SPIR) coronal postcontrast T1-weighted image (C) enables better contrast between enhanced spinal ganglia (arrow) and surrounding fat-suppressed fat tissue signal compared with corresponding non-SPIR image (D).

fig 3.

Light microscopy of the sural nerve specimen (Toluidin blue stain, semi-thin section) in a patient with CMT I and atypical clinical symptoms (case 3). Almost all fibers show “onion bulbs” (black arrowhead), with an absence of myelinated fibers, indicating active demyelination. Clusters of regenerating fibers are indicated by thin black arrow and collagen hypertrophy by large black arrow.

fig 4.

A and B, LM and EM of the sural nerve specimen (Toluidin blue stain, semi-thin section) in a patient with the congenital hypomyelinating form of DSD (case 8). On LM (A), a decreased number of myelinated fibers with peri- and epineural connective tissue hypertrophy is noted (arrow). Very few residual thinly myelinated fibers (open black arrow) are observed. Note the absence of onion bulbs and connective tissue hypertrophy (thick black arrows) with fibroblasts (black arrowhead). On EM (B), complete absence of myelin sheaths around axons is seen. A Schwann cell nucleus is indicated by the arrow.