A unilateral cavus deformity of the foot suggests the possibility of an intraspinal lesion such as diastematomyelia or tethered cord syndrome. We report the case of a child who had a progressive equinocavovarus deformity of the foot secondary to a neuromuscular choristoma (hamartoma) involving the sciatic nerve.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Department of Pediatric Orthopaedics, St. Louis Children's Hospital, Washington University School of Medicine, One Children's Place, St. Louis, Missouri 63110-1077.
‡Childrens Hospital Los Angeles, University of Southern California School of Medicine, 4650 Sunset Boulevard, Los Angeles, California 90027.
An eight-year-old boy was referred to us for the evaluation of a painless, progressive unilateral cavovarus deformity of the right foot and a limp. The child was the product of a full-term, uncomplicated pregnancy; he had weighed nine pounds (4.1 kilograms) at birth and had been delivered vaginally. The developmental milestones were normal, and the child had walked independently when he was one year old. The parents first noticed a deformity of the right foot when the boy was four years old, but they did not seek medical attention until he was eight years old. The deformity had progressed in the interim, and the child appeared to have weakness of the affected extremity and a limp at the time of presentation. He did not complain of pain. There was no family history of a neurological disorder.
Physical examination revealed that the spine and the upper extremities had a normal appearance and a full range of motion, and the results of a neurological examination were normal. The entire right lower extremity was atrophied: the circumferences of the right thigh and calf were two centimeters smaller than those of the left thigh and calf. The range of motion of both hips was symmetrical. There was a 10-degree flexion contracture of the right knee with further flexion to 140 degrees. In addition, there was an equinocavovarus deformity of the right foot. The range of motion of the ankle was -15 to 45 degrees of plantar flexion. The hindfoot was in 15 degrees of varus with no passive subtalar motion. The forefoot was adducted 15 degrees, and the first metatarsal was fixed in plantar flexion and pronation. Muscle strength was decreased to grade 4 (of 5) in the quadriceps, the hamstrings, the posterior tibial muscle, the gastrocnemius muscle, the soleus muscle, and the flexors of the toes and to grade 2 in the anterior tibial muscle, the peroneal muscles, and the extensors of the toes. The patient had normal sensation to touch, pain, and position in both lower extremities. The patellar reflex was normal bilaterally, and the Achilles reflex was decreased on the right.
Posteroanterior and lateral radiographs of the spine, made with the patient standing, revealed normal findings. Radiographs of the right foot showed an equinocavovarus deformity. Electrodiagnostic studies of the lower extremities showed neuropathic changes on the right, with prolonged latency of the peroneal nerve (10.4 milliseconds on the right, compared with 3.84 milliseconds on the left), decreased conduction velocity of the posterior tibial nerve (37.0 milliseconds on the right, compared with 62.5 milliseconds on the left), and a neuropathic recruitment pattern. Magnetic resonance images of the cervical, thoracic, and lumbar spine revealed normal findings. Magnetic resonance images of the pelvis showed a soft-tissue mass that extended posterolaterally from the inner wall of the right side of the pelvis through the sciatic notch, parallel to the sciatic nerve, to the level of the ischial tuberosity (Figs. 1-A, 1-B, 1-C and 1-D). The mass had the same signal intensity as muscle on T1 and T2-weighted images, and it had infiltrated the piriformis muscle. The images showed atrophy of the right gluteus maximus, gluteus medius, and obturator internus muscles.
The mass was explored through a posterior gluteus maximus-splitting approach and was found to be three by eight by 2.5 centimeters in size. The mass was adherent to the sciatic nerve and had the appearance of pale muscle. A nerve-stimulator was inserted at a variety of locations in the mass, and muscle contractions were observed in the posterior compartment of the thigh and in the anterior and posterior compartments of the leg. Three specimens, one by one centimeter in size, were obtained from different locations within the mass. Examination of the frozen sections revealed elements of both skeletal muscle and nerve tissue without any evidence of malignant change.
The tissue specimens were embedded in paraffin, and the sections were stained with hematoxylin and eosin, trichrome, and S-100. The sections showed abnormal mature skeletal muscle and tortuous nerve trunks that lacked a stratified arrangement. In some areas, the muscle had a nodular configuration and a spindle-like appearance (Fig. 2). There was a marked and variable increase in perimysial and endomysial fibrous tissue, and several irregular fascicles of various sizes were visualized. The S-100 stain highlighted the abnormal distribution of nerve trunks (range, eight to fifty micrometers in diameter) that were embedded within the connective tissue. In some areas, these nerve trunks completely surrounded individual muscle fascicles (Fig. 3). There were one to four nerve trunks per high-power field. Enzyme histochemistry with use of adenosine triphosphatase (pH 9.4 and 4.6) showed a predominance of type-I fibers. There was no evidence of adipose or vascular tissue.
Four weeks later, the patient had a reconstructive procedure to correct the deformity. The operation involved lengthening of the Achilles tendon, a plantar fasciotomy, an osteotomy of the first metatarsal, a Jones procedure, a lateral closing-wedge osteotomy of the calcaneus, and transfer of the posterior tibial tendon through the interosseous membrane. Eighteen months after the operation, the patient was free of pain and had a plantigrade foot without recurrent deformity. The neurological status was the same as it had been preoperatively.
Neuromuscular choristomas or hamartomas are benign tumors composed of skeletal muscle and neural elements that generally occur in young children. In our review of the literature, we found reports on only ten patients who had such a lesion; nine of these patients were two years old or less at the time of diagnosis1-7. Most of the lesions were solitary and involved the brachial plexus or the sciatic nerve. The etiology remains unknown.
Louhimo and Rapola described the cases of two patients who had an intraneural muscular hamartoma. The first patient was a twenty-one-month-old boy who had a three-centimeter-diameter mass in the supraclavicular fossa. The mass, which arose from the brachial plexus, was excised and did not recur. The second patient was a four-month-old boy who had a subcutaneous mass in the posterior portion of the thigh; the mass was found to be attached to the sciatic nerve and was excised. Neither patient had a neurological deficit either preoperatively or postoperatively. Histologically, both lesions were composed of mature skeletal muscle and nerve fibers.
Markel and Enzinger reported their experience with two patients. The first patient was a five-month-old girl who had a hamartoma that involved the brachial plexus. The patient had no neurological deficits at the time of the initial examination, but ulnar and median-nerve palsies developed after an attempted excision of the tumor. Re-exploration of the brachial plexus four months later did not reveal any residual tumor. By the fourth postoperative year, the child had regained most of the function of the muscles of the upper extremity but still was unable to flex the index finger. The second patient was a two-year-old boy who had a hamartoma that was attached to the sciatic nerve; the patient had paralysis of the posterior tibial and gastrocnemius muscles at the time of presentation. The tumor could not be excised completely, and the final outcome could not be determined because the patient was lost to follow-up after discharge from the hospital.
Bonneau and Brochu reported the tumor in two patients. The first patient was a six-year-old girl who had a hamartoma that involved the brachial plexus. A neurological deficit developed after an attempted excision. The second patient was a fourteen-year-old girl who had a small neuromuscular hamartoma that arose from the intercostal nerves in association with recurrent musculoaponeurotic fibromatosis of the axilla.
Chen reported on one patient who had a neuromuscular hamartoma that arose from the median nerve in the axilla. The clinical details were not reported. The fusiform mass was adherent to the nerve but was easily separated at the time of the operation. A recurrent mass was noted soon after the operation, but it had not increased in size by the fourth postoperative year. Six months later, at the time of re-exploration, the mass was seen to be attached to the median nerve. Resection of the mass was not attempted because it would have necessitated sacrifice of the nerve. A biopsy revealed dense fibrous tissue.
Zwick et al. reported the case of a twenty-nine-month-old boy who had an intracranial neuromuscular hamartoma that involved the trigeminal nerve. The mass was composed primarily of skeletal muscle fibers interspersed with nerve fibers. Despite the relative paucity of neural elements, this lesion was considered to be a neuromuscular choristoma because mature skeletal muscle tissue was present within the nerve trunk. O'Connell and Rosenberg reported the case of a three-month-old girl who had two polypoid skin nodules; both lesions had an identical histological appearance and were composed of mature skeletal muscle cells mixed with nerve fibers. The nodules did not arise from a major peripheral nerve trunk.
Our patient had a unilateral deformity of the foot secondary to a large neuromuscular hamartoma that involved the sciatic nerve. Resection of the mass was not feasible because it would have resulted in an increase in the neurological deficits. The natural history of this benign lesion is indeterminate. It is not known whether the neurological deficits are due to tethering of the sciatic nerve by the mass or to an injury of the remaining normal neural elements by either progressive infiltration of the nerve or compression by the mass effect of the tumor itself. Fortunately, the neurological deficits in our patient had not progressed by the time of the latest follow-up evaluation. The findings of the present study emphasize the need for the careful evaluation of a patient who has a unilateral deformity of the foot.