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MR Imaging in the Differential Diagnosis of Neurogenic Foot Drop

Martin Bendszusa, Carsten Wessigb, Karlheinz Reinersb, Andreas J. Bartscha, Laszlo Solymosia and Martin Koltzenbergb

a Department of Neuroradiology, University of Würzburg, Würzburg, Germany
b Department of Neurology, University of Würzburg, Würzburg, Germany



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  		FIG 1. Electrophysiologic and MR changes in common peroneal nerve palsy.

A, Axial T1-weighted image localizes affected muscles. TA indicates the anterior tibial muscles; ED, the extensor digitorum; and PL, the long peroneal muscle. No abnormalities are shown.

B, Axial TIRM image depicts increased signal intensity in the TA, ED, and PL muscles, a pattern compatible with a common peroneal nerve lesion.

C, EMG recording shows spontaneous activity in the TA and PL muscle; in the posterior tibial (TP), there is normal insertional activity.

D, On stimulation of the distal peroneal nerve, no compound muscle action potential (CMAP) can be recorded in the extensor digitorum brevis muscle of the foot.



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  		FIG 2. Electrophysiologic and MR changes in L5 nerve root lesion.

A, Axial T1-weighted image localizes affected muscles. No abnormalities are evident.

B,Axial TIRM image reveals a signal intensity increase in the TA, ED, PL, TP, and popliteus (P) muscles. This pattern was consistent with an L5 nerve root lesion.

C, EMG shows spontaneous activity in the TA, extensor hallucis longus (EHL), and TP muscles; as with MR results, these findings are consistent with a lesion of the L5 root.

D, Nerve conduction studies of the peroneal nerve show normal CMAP after stimulation of the peroneal nerve, at the level of the ankle, distal and proximal to the fibular head (amplitude, 9 mV; nerve conduction velocity, 50 m/s). In this patient, a lumbar disk herniation was confirmed at surgery.



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  		FIG 3. MR images obtained in a patient who had partial sciatic nerve damage of nonspecific pattern after a motorcycle accident.

A, Axial T1-weighted localizes affected muscles.

B, Axial TIRM image shows high signal intensity in the TA, ED, and medial head of the gastrocnemius (GM) muscles.



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  		FIG 4. MR images obtained in a 35-year-old male patient who presented with a 2-month history of left-sided sciatica due to lumbar disk herniation. MR imaging revealed a more widespread involvement of muscles of nonspecific pattern than did routine EMG (not shown).

A, Axial T1-weighted image localizes affected muscles.

B, Axial TIRM image not only shows signal intensity increase in the TA, ED, PL, P, and TP muscles (L5 radicular pattern), but also in the lateral head of the gastrocnemius (GL) muscle.

EMG studied only the medial head of the GL; no neurogenic changes were found, and the diagnosis of an L5 nerve root compression was made. CT of the lumbar spine revealed a large disk herniation compressing both the L5 and S1 nerve root (not shown) that were subsequently confirmed at surgery.



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  		FIG 5. MR images obtained in a 42-year-old female patient who presented with a foot drop after splint fixation around the proximal lower leg. This case exemplifies that MR imaging is capable of demonstrating the entire muscle, whereas EMG can only study parts of a muscle.

A, Axial T1-weighted image obtained just below knee level localizes affected muscles.

B, Axial TIRM image obtained at the level of A does not show signal intensity abnormality.

C, Axial T1-weighted image obtained approximately 4 cm below knee level localizes affected muscles.

D, Axial TIRM image obtained approximately 4 cm below knee level shows marked signal intensity increase in the TA, ED, and PL, findings consistent with a peroneal nerve lesion.

Initial needle EMG (not shown) obtained just below the knee level did not reveal denervation; however, follow-up examination further distally showed marked denervation in the TA, ED, and PL muscles.





Copyright © 2008 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X