About a Rare Case of Chronic Ankle Pain: Unusual Localization of the schwannoma

Schwannoma in the lower limb is extremely rare and only few cases were reported., they are often overlooked in the first diagnosis and often confused with other common lesions in this localization. Herein we report a 62 years old man who presented pain and paresthesia on the lateral aspect of the ankle since 3 months. The clinical and radiological finding prompting the patient to undergo surgery in which an excisional biopsy of the mass of the leg was realized. The post-operative was uneventful. Two weeks later, the histopathological analysis was in favor of schwannoma with a good result at the last follow up. At last, we emphasis that schwannoma should be considered as a possible diagnosis in patient with chronic ankle pain, particularly if all other injury has been ruled out which can raises the awareness about this tumor.


INTRODUCTION
Schwannoma is a benign peripheral nerve sheath tumor originating from Schwann cells that slowly grows eccentrically to the nerve axis. It accounts for only 5% of all soft tissue tumors. [1] It is frequent in the head and neck region. [2] Therefore, they occur rarely in the lower limb and only a few cases were reported. [3] Moreover, given the lack of awareness, they are often overlooked in the first diagnosis and often confused with other common lesions in this localization such as lipoma. Herein we report our second patient of a rare localization of the schwannoma of the leg and how it was managed.

CASE PRESENTATION
A 62 years old man with no disease's history, presented pain and paresthesia on the lateral aspect of the ankle since 3 months. He made many consultations in which at every time he got an anti-inflammatory drug, oral's analgesic and rest advised that partially calmed the pain. Therefore, a few days following the end of treatment, he experienced the same pain at the same localization becoming permanent which irradiated to the foot, the reason why he consulted our orthopedic department. On admission, both the physical examination of the ankle and the neurovascular exam were normal. However, at 5 cm above the lateral aspect of the ankle, we noted a mobile mass of 2 cm /1cm. The plain radiograph was normal. The ultrasound showed a markedly hypoechoic mass with increased through-transmission of sound deep to the lesion which suggested a schwannoma or lipoma and requested a complemented magnetic resonance imaging (MRI) (Figure 1).
Given the patient's financial conditions, the MRI was not performed. A few days later, the patient underwent surgery for an excisional biopsy of the mass (Figure 2).
The post-operative was uneventful. Two weeks later, the histopathological analysis was in favor of schvannoma (Figure 3) At the last follow up of 18 months, the patient did well with no recurrent of pain.

DISCUSSION
Schwannomas are benign nerve sheath tumors that originate from Schwann cells. They may be seen at all ages, but occur predominantly in the 20-to 50-year age group. tion and is confirmed by biopsy or pathological analysis of the operative specimen [7] In the majority of cases, schwannomas can be easily enucleated through microsurgical dissection without damaging the nerve contiguity [3] Most patients with a small solitary schwannoma are managed nonoperatively except if they manifest a progressive neurological deficit, pain, need for tissue diagnosis, or growth on serial imaging. Our case presented a chronic pain of the leg which prompting the patient to undergo surgery. [8] A. Goyal, "Benign and malignant tumors of the peripheral nerve," in Youmans and Winn Neurological Surgery, Elsevier, 7 edition, 2017, Chapter: 258. Histologically, the neoplasm is characterized by encapsulation and is composed of Antoni A and B cells and Verocay bodies [9] Immunohistochemistry shows that S-100 stain was positive [10] CONCLUSION Given that the chronic ankle pain is a frequent complaint of elderly patient, we emphasis that schwannoma should be considered as a possible diagnosis in patient with chronic ankle pain particularly if all other injury has been ruled out which can raises the awareness about this rare entity and so leading to an early diagnosis of schwannoma which may prevent permanent nerve damage, soft tissue or boney deformity.

ACKNOWLEDGMENTS
We want to acknowledge Mme Houria Khourchech for her helpful revision of the English language.

CONSENT FOR PUBLICATION
Consent was obtained from the patient for publication of this case report and accompanying images.  No gender predilection is noted. [4] Their size ranges from about 2-20cm in diameter with the smaller tumors appearing white, fusiform, round and firm. The larger tumors are usually irregular, lobulated and grey or yellowish-white [5]. As a complication, it may cause nerve damage, soft tissue or boney deformity. The main differentials diagnosis are ganglion cysts, lipomas and lipofibromatous hamartomas are usually easily compressible and soft to touch, whereas neoplastic tumors, like schwannomas, are firm to touch [6] Diagnosis can be suggested on US, CT, and MRI examina-a b Figure 3. Histological section showed that the tumors cells are regular spindle-shaped palisades (HEx200)