Foot Drop due to Cranial Gunshot Wound

Military Medicine, Jul 2004 by Atac, Kaan, Ulas, Umit Hidir, Erdogan, Ersin, Gokcil, Zeki

Objective: We present a case of foot drop from hemorrhagic contusion after cranial gunshot, which has never been reported. Methods: A 21-year-old man was admitted with inability of dorsiflexion 1 day after a tangential gunshot wound of the scalp. The scalp skin was cut by the rifle bullet. He had foot drop and his neurological examination was normal except for weakness at dorsiflexion of the right foot. Pathological reflexes and sensation failure were not detected. T1- and T2weighted magnetic resonance images showed hyperintense contusion at the right superior frontal gyrus and mild subdural hemorrhage. Peripheral nervous system examination was electrophysiologically normal. Motor-evoked potentials showed the location of the lesion at the motor cortex because no electrical record was obtained from the right anterior tibial and extensor digitorum brevis muscles, and there was a normal record on the left. Six months later, the patient's neurological examination was uneventful. Conclusion: When a cranial gunshot wound injury victim presents with foot drop, the central causes should be included in the differential diagnosis list.

Introduction

Lumbar disc pathologies are the most frequent etiology in foot drop. Foot drop secondary to brain lesions are rarely seen in practice. Brain tumors, traumatic lesions, and infections may cause permanent or temporary findings.1-3

We describe a patient who had temporary right foot drop after a nonpenetrating tangential cranial bullet injury. A hemorrhagic precentral gyrus contusion just located on the knee of the inverted homunculus causing drop foot was revealed.

Case Report

A 21-year-old man was admitted with inability of dorsiflexion 1 day after a tangential gunshot wound of the scalp. The scalp skin was cut by a rifle bullet. Macroscopically, there was an open scalp wound over the 2 cm behind the middle of the vertex. The scalp wound length was 3 cm and did not pass the superior sagittal suture. There was a sharp fracture line over the bone with palpation. The angle of the bullet was most likely parallel to the scalp wound because there was only an entry wound. He had foot drop and his neurological examination was normal except for weakness at dorsiflexion of the foot. No pathological reflexes or sensation failure was detected.

Lateral craniography showed cortical discontinuation at the inner table. Cranial computed tomography revealed a hemorrhagic contusion in the right parietal lobe. T1- and T2-weighted magnetic resonance images showed a hyperintense contusion at the left superior frontal gyrus and a mild subdural hemorrhage (Figs. 1 and 2).

There was not any abnormal finding on motor and sensory conduction of the peroneal nerve and F response latencies with needle electromyography and nerve conduction study. There was not any response from the right anterior tibial and extensor digitorum brevis muscles on magnetic stimulation study when stimulated on vertex. The responses from lumbar and cervical regions were normal on a tibial nerve somatosensory-evoked potential test. His monthly periodical examination showed that the neurological deficit cleared gradually. Six months later, the patient's neurological examination was uneventful.

Discussion

Foot drop secondary to entrapment of the nerve at the fibula head, L5 disc pathologies or compression of the spinal root by space-occupying lesions are the most frequent clinical presentation. Traumatic or tumoral peripheral nerve lesions may be the cause of foot drop as well. The absence of neurological examination and/or imaging findings for lumbar or peripheral pathologies should remind the central causes on motor stripe. Additional symptoms such as hyperreflexia, headache, and Babinski's sign are diagnostically helpful.3 Hypoestesia may not be present if lesions were not harmful for postcentral gyrus.

Brain traumas may present as localized peripheral nerve findings.1 A nonpenetrating high-velocity bullet has a kinetic energy, causing blast injury in a limited area. In this case, pinpoint contact of the bullet with the skull created a small hemorrhagic contusion of the motor cortex. It was obvious that the patient had a brain trauma, but the localization of the nerve injury was crucial.

No doubt, it is easy to make the precise identification of damage nature and location by history and simple imaging tools. However, even if the diagnosis was obvious, imaging and electrophysiologic studies are vital in identifying, characterizing, and following patients.

Motor-evoked potentials showed the location of lesions at the motor cortex because there was no electrical record obtained from the right anterior tibial and extensor digitorum brevis muscles, and there was a normal record on left. The exact location of the lesion on the superior frontal gyrus that supplementary motor area (SMA, area 6) presents was revealed by axial magnetic resonance images. SMA contains a topographic representation of the body with the head located in the anterior portion of SMA and the legs and feet in the posterior part, adjacent to area 4. Mild motor deficits after a hemorrhagic cortical contusion may be explained by this location because SMA drives upper motor neurons in the primary motor cortex, but the corticospinal projections form SMA terminate principally on spinal interneurons and not directly on lower motor neurons.