July/August 2006 ⢠Vol 96 ⢠No 4 ⢠Journal of the American Podiatric Medical Association. Schwannomas are benign tumors that arise from pe- ripheral nerves ...
CLINICALLY SPEAKING
Foot Schwannomas That Mimic Nerve-Entrapment Syndromes A Report of Three Cases Pedro Carpintero, PhD* Emilio Gascón, MD* José Antonio Abad, MD* Manuel Ruza, MD† Schwannomas of the foot are rare. We describe three cases that mimicked compressive neuropathy, two resembling tarsal tunnel syndrome and a third resembling Morton’s neuroma. All three patients had complete resolution of their pain after resection of the tumor. (J Am Podiatr Med Assoc 96(4): 344-347, 2006)
Schwannomas are benign tumors that arise from peripheral nerves with a Schwann cell sheath. Schwannomas of the foot have rarely been reported, with approximately 30 cases described in the literature.1-3 They are usually located on the flexion surface of the limbs4 and tend to be solitary lesions, although multiple lesions are occasionally reported.5, 6 Schwannomas may occur in the subcutaneous, intramuscular, intermuscular, or intraosseous planes. The symptoms are a matter of debate. Some authors report that the schwannoma is usually asymptomatic and that clinically it presents as a slow-growing soft-tissue tumor with occasional neurologic symptoms, such as altered sensation or motor weakness,1, 3, 5, 7, 8 or that pain arises only when the mass exceeds 5 cm.9 Other researchers, however, report that most schwannomas prompt local or radiating pain (or both) and a positive Tinel sign.4 The pain sometimes resembles that associated with tarsal tunnel syndrome10, 11 or Morton’s neuroma.3, 12 There is no sex predilection for schwannomas, and although they may occur at any age, they are commonly found during the fourth decade of life.13 The lesions grow slowly at the periphery of the nerve *Orthopaedic Department, University Hospital “Reina Sofia,” Cordoba, Spain. †Radiology Department, University Hospital “Reina Sofia,” Cordoba, Spain. Corresponding author: Pedro Carpintero, PhD, Mejorana 45, 14012 Cordoba, Spain.
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sheath, without invading the interior of the nerve. The treatment of choice for these lesions is excision; because malignant transformation is rare, wide excision is not indicated. Tumor removal does not jeopardize the integrity of the nerve and can result in relief of symptoms and maintenance of nerve function.7, 12, 14 There are, however, reports of neurologic complications after excision of a schwannoma, including pain and muscle weakness.15 We describe three cases that mimicked compressive neuropathy, two resembling tarsal tunnel syndrome and a third resembling Morton’s neuroma. All three patients had complete resolution of their pain after resection of the tumor.
Case Reports Case 1 A 48-year-old woman presented for evaluation of a mass on the plantar aspect of her left foot. She first became aware of the mass 2 years earlier but had felt no pain until 1 month before consultation, when weightbearing elicited pain that radiated toward the toes. Examination showed a 2.5 × 1.5-cm firm mass on the medial plantar aspect of the left foot. It was moderately tender on deep palpation, and there was evidence of partial numbness on the plantar aspect of the first and second toes. Results of radiographic
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examinations of the left foot were negative. Magnetic resonance imaging of the same foot showed a 4 × 2-cm clearly defined mass embedded in the plantar musculature (Fig. 1). Surgery was performed under regional anesthesia and a thigh tourniquet was used. A well-encapsulated mass adhering to the medial plantar nerve was dissected from the nerve and excised. On histologic examination, the mass was identified as a benign schwannoma. Hematoxylin and eosin staining exhibited numerous nuclei in a palisade arrangement (Antoni A pattern) (Fig. 2). Three years later, the patient had no sign of a mass and no painful foot symptoms.
Case 2 A 46-year-old woman presented for evaluation of a mass on the medial aspect of the ankle and sole of her left foot. The mass was first noticed 2 months earlier, coinciding with pain that radiated toward the medial aspect of the foot and first toe. The pain was intense, obliging the patient to assume an antalgic gait, and was present even at rest, particularly in bed at night. Examination of the foot and ankle showed a 5 × 3-cm mass on the medial aspect of the ankle and sole. The mass was tender on deep palpation, and Tinel’s sign was present; there was also evidence of numbness on the plantar aspect and the first and second toes. Magnetic resonance imaging of the foot disclosed a clearly defined mass embedded in the plantar musculature close to the calcaneus (Fig. 3). As in Case 1, surgery was performed under regional anesthesia and a thigh tourniquet was placed. A well-encapsulated lobular mass adhering to the posterior tibial nerve was dissected from the nerve and ex-
Figure 2. Hematoxylin and eosin staining (×200) exhibiting numerous nuclei in a palisade arrangement (Antoni A pattern).
Figure 3. Sagittal T1-weighted image of the left foot showing a mass isointense to muscle involving the plantar musculature near the calcaneus.
cised. On histologic examination, the mass was identified as a benign schwannoma. Hematoxylin and eosin staining exhibited numerous nuclei in a palisade arrangement (Antoni A pattern) (Fig. 4). The pain subsided during the postoperative period, and 18 months later the patient displayed no sign of a mass or painful symptoms.
Case 3 Figure 1. Sagittal gradient-echo T2-weighted image of the left foot showing a clearly defined mass with high signal intensity located in the plantar musculature.
A 57-year-old man presented with persistent pain in the ball of his right foot that radiated into the second
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Figure 4. Hematoxylin and eosin staining (×200) exhibiting numerous nuclei in a palisade arrangement (Antoni A pattern).
and third toes. Ultrasonographic examination disclosed a hypoechoic mass under the second and third metatarsal heads (Fig. 5). Magnetic resonance imaging of the foot showed a rounded, clearly defined mass under the second and third metatarsal heads, leading to an initial diagnosis of Morton’s neuroma (Fig. 6). During surgery, under regional anesthesia and using a thigh tourniquet, a slightly lobular mass measuring approximately 2 cm was dissected from the interdigital nerve to which it adhered. At histologic examination, the mass was identified as a benign schwannoma. Hematoxylin and eosin staining exhibited numerous nuclei in a palisade arrangement (Antoni A pattern) (Fig. 7).
Figure 5. Ultrasonographic scan showing a hypoechoic mass measuring approximately 2 cm.
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Figure 6. Coronal spin-echo T1-weighted image of the right foot showing a small mass under the second and third metatarsal heads.
Discussion In the three cases of schwannoma reported here, the main symptom was pain, although in two patients the tumor measured less than 5 cm; this may be because the location of the mass on the plantar aspect of the foot more readily prompted irritation due to weightbearing. Two patients displayed symptoms resembling those of tarsal tunnel syndrome, whereas in the
Figure 7. Photomicrograph of a specimen from Case 3 (H&E, ×200). These findings are similar to those of the other cases (Antoni A pattern).
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third patient clinical signs were more reminiscent of Morton’s neuroma. In all three patients, the tumor was located on a flexor surface, as in most of the cases reported in the literature4; the mass was a solitary finding, as is also usually the case, although multiple lesions are occasionally reported.5, 6 The age of our patients also matched that of other cases reported in the literature,13 with the lesion appearing in the fourth decade of life in two of our patients. Although schwannomas may occur in the subcutaneous, intramuscular, intermuscular, or intraosseous planes, the location was intramuscular in the three cases reported here. Differential diagnosis should include other potentially painful tumors,11 radiculopathy,9 and, in the foot, tarsal tunnel syndrome and Morton’s neuroma; as the published literature illustrates, many schwannomas in the lower limb prompt symptoms that resemble those reported in these nerve-entrapment syndromes.11, 12 The initial diagnosis in the cases reported here was compression neuropathy. In all three patients, simple removal of the tumor led to the disappearance of all symptoms, with no tumor recurrence. In conclusion, as Liebau et al13 suggested, although schwannomas are rare, they should be considered in all cases of pain and paresthesia of the foot when other possible sites of injury have been ruled out.
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