CASE REPORT


https://doi.org/10.5005/jp-journals-10040-1306
Journal of Foot and Ankle Surgery (Asia-Pacific)
Volume 11 | Issue 1 | Year 2024

Giant Schwannoma of Foot: A Report of Two Cases and Literature Review


Siddharth Gupta1, Ankit Khurana2https://orcid.org/0000-0001-8397-6903, Karan Jaggi3, Dheeraj K Singh4, Raskesh Malhotra5, Karan Rajpal6

1Department of Orthopaedics, Adarsh Multipespeciality Hospital and Trauma Centre (AMHTC), Delhi, India

2,6Department of Orthopaedics, Dr. Baba Sahib Ambedkar Medical College and Hospital, Delhi, India

3Department of Orthopaedics, Vaidyam Bone & Joint Centre, Delhi, India

4Department of Pulmonology, Adarsh Multipespeciality Hospital and Trauma Centre (AMHTC), Delhi, India

5Department of Orthopaedics, Guru Teg Bahadur Hospital, University College of Medical Sciences (UCMS), Delhi, India

Corresponding Author: Ankit Khurana, Department of Orthopaedics, Dr. Baba Sahib Ambedkar Medical College and Hospital¸ Delhi, India, Phone: +91 8437029392, e-mail: ankit24388@gmail.com

Received: 21 September 2022; Accepted: 02 May 2023; Published on: 30 December 2023

ABSTRACT

Schwannomas are benign, isolated, and encapsulated tumors originating from schwann cells of the peripheral nerve sheath. Schwannomas usually affect the head and neck region and localization in the lower extremity is exceptionally rare with a reported prevalence rate of 1–10%. A <20 cases of schwannomas of feet have been reported in the literature, most commonly causing compression in the tarsal tunnel, it is however rare for them to be seen more distally. We herein report a rare presentation of giant schwannoma of the foot diagnosed on either a magnetic resonance imaging (MRI) scan or ultrasound scan of the foot which revealed a well-defined, lobulated soft tissue lesion likely of fibrous or neural origin. Both patients underwent an excisional biopsy under spinal anesthesia, with an uneventful recovery period. The postoperative (post-op) follow-up was reported to be normal with no radiological evidence of recurrence. This report of two cases and the included literature review aims to highlight the diagnostic challenges of this rarely encountered entity and the authors hope to raise awareness of lower limb schwannomas and their clinical presentation.

How to cite this article: Gupta S, Khurana A, Jaggi K, et al. Giant Schwannoma of Foot: A Report of Two Cases and Literature Review. J Foot Ankle Surg (Asia-Pacific) 2024;11(1):25–28.

Source of support: Nil

Conflict of interest: None

Keywords: Ankle, Benign, Case report, Foot tumors, Tibial nerve

INTRODUCTION

A schwannoma or neurilemmoma is a noncancerous, solitary, noninvasive, and encapsulated growth that arises from the schwann cells found in the peripheral nerve sheath.1 The schwannomas follow an indolent course. Acoustic neuroma is the most common type of schwannoma.2 Schwannomas in the foot and ankle are uncommon, with a prevalence rate ranging from 1 to 10%.1 A schwannoma typically develops in individuals aged 20–50 and rarely undergoes a malignant transformation.3 It is estimated that only 1% of cases have malignant potential.4,5

A schwannoma is a type of tumor that originates from the nerve sheath and is typically a soft-tissue tumor. While it is rare for schwannomas to occur in the foot, they are typically benign and seldom malignant.6,7 Schwannomas typically affect the head and neck area, and it is extremely rare for them to occur in the lower extremities.8 Furthermore, only a small number of cases have been reported of schwannomas occurring specifically in the foot.9 The utilization of MRI can facilitate early detection and furnish significant data about the tumor’s dimensions and whether it has infiltrated the bone. In these two cases, it was observed that the complete removal of the schwannoma, irrespective of its magnitude, can avert the possibility of local recurrence.

We report two cases of a giant schwannoma of the foot diagnosed in young men. The patients were followed up for a post-op period of over 18 months. The follow-up was unremarkable with no radiological evidence of recurrence.

CASE DESCRIPTION

Case 1

A 27-year-old man, visited the clinic with a complaint of a painless soft tissue lump on the dorsomedial part of his left foot (as shown in Fig. 1). The patient first noticed the lump a few years prior to his visit and did not recall any foreign body, puncture wound, or injury causing the swelling. The swelling had been gradually increasing in size and was almost painless throughout its course. The patient had difficulty wearing shoes because of the swelling.

Figs 1A to D: (A) Preoperative clinical appearance on the superomedial aspect of the foot; (B and C) Radiographs taken in two orthogonal planes; (D) MRI showing well-defined and lobulated soft tissue signal intensity lesion along the superomedial aspect of the left hindfoot, comprising of solid-cystic components and few intralesional septations

During clinical examination, the patient appeared to be healthy without any obvious discomfort. The swelling was firm to hard in texture, painless, and seemed to be unconnected to the underlying tissues/bone. It did not appear to be associated with any extensor tendons of the digits and no callus formation or trophic changes were observed over the soft-tissue mass. There were no visible associations with any superficial vessels. The entire mass could be clearly observed clinically with plantar flexion of the digits, owing to its superficial anatomical location (Fig. 1A).

The patient did not report any other symptoms besides the main concern of a painless, palpable soft-tissue mass on the dorsomedial aspect of his left foot. Vascular examination showed normal pedal pulses and neurological examination revealed normal cutaneous responses and reflexes. The foot did not have any deformities and the gait was normal without limping.

Radiographs were taken during the first visit, which did not reveal any soft-tissue calcification, subdermal lucency, or periosteal reaction near the soft-tissue mass (Figs 1B and C). Possible diagnoses were discussed, including ganglion cyst, fibroma, neuroma, lipoma, and in rare cases, a soft-tissue tumor. To further investigate, an MRI of the left foot was performed on an extremity coil (1.5 Tesla Signa HD-GE Medical System).

The MRI revealed a well-defined and lobulated soft tissue signal intensity lesion (Fig. 1D) along the superomedial aspect of the left hindfoot, comprising solid-cystic components, and few intralesional septations. The lesion extended along the subcutaneous planes and appeared abutting the underlying extensor tendons and neural elements, likely of fibrous/neural origin. An attempt of aspiration under local anesthesia failed to give any diagnostic or therapeutic results.

The patient was then offered surgery in the form of an excisional biopsy. After taking the due consent from the patient the patient was operated on under spinal anesthesia with the patient lying in the supine position and a pneumatic tourniquet was inflated at 100 mm Hg higher than the systolic blood pressure which was taken at the arm. A surgical incision measuring 7 cm in length and in a linear longitudinal direction was created to expose the swelling on the dorsomedial part of the patient’s left hindfoot. As soon as the subcuticular layer was opened, the mass was observed. It was fully encapsulated, did not appear to be associated with any vascular or tendinous structure, and did not seem to extend deep or horizontally into the surrounding tissue. The tumor was carefully dissected and removed (Figs 2A2C) so as to make sure that the lesion is removed en bloc (Figs 2C and D) with no traces being left behind and was sent for histopathological evaluation. The mass measured approximately 61 × 34 × 25 mm in size. Intraoperatively it appeared to be a soft tissue tumor and unlikely to be a ganglionic cyst.

Figs 2A to E: (A and B) Showing surgical incision and meticulous dissection of the lump; (C) En bloc removed the tumor with no capsular breach; (D) Showing surgical closure; (E) Histopathological appearance of the tumor showing classical features in hematoxylin and eosin

The pathology report on gross examination indicated a pale red soft tissue piece, soft to firm in consistency. The histopathological examination showed a biphasic cellular pattern consisting of hypercellular areas with nuclear palisading and hypocellular areas with a loose stroma (i.e., the so-called Antoni A and B areas, respectively), which is typical of schwannoma (Fig. 2E).

The post-op recovery was unremarkable. The patient was able to walk the next day and was nearly painless. The incision healed with a clean flat scar and without any paresthesias. The patient had been in our regular follow-up for a post-op period of 26 months. There was no clinical evidence of recurrence of soft tissue mass. The MRI was performed at the end of the 6 months, which did not show any radiological evidence of recurrence. The tumor was superficial in location and therefore it was difficult to ascertain the tiny branch of the nerve from which the schwannoma originated.

Case 2

The second patient was a 20-year-old male who presented with painless gradually progressive swelling of the posterolateral aspect of the ankle. The same was present for nearly 3 years and had progressed to its current size (Figs 3A and B). An ultrasonogram was carried out which suggested a ganglion cyst. On excision, however, the mass seemed to arise from the sural nerve and histopathology revealed the said lump to be a schwannoma. The excised tumor was 57 × 44 × 15 mm in size. The patient had an unremarkable recovery and after 18 months had no evidence of recurrence or symptoms.

Figs 3A to B: (A) Showing surgical dissection of the tumor mass; (B) Showing surgical closure after complete removal

DISCUSSION

This report describes two cases of a giant schwannoma of the foot, thus being clearly atypical for both localization and size. The average length of a schwannoma in the foot or ankle is 1.5–2 cm.10Table 1 shows the anatomical distribution of schwannomas, as described in a cohort study by Das Gupta et al.11 Only 11% of all the cases were reported in the lower extremity. Of these, only 3.5% were found in the ankle and none in the foot (Table 1).

Table 1: Benign neurilemmoma (schwannoma)
Main anatomic locations (303 patients)
Head and neck 136
Upper extremity 58
Trunk 36
Lower extremity 41
Miscellaneous 42

Schwannomas of the foot are a rare occurrence with <20 cases reported in the literature. They are typically associated with compression in the tarsal tunnel, but distal occurrences are uncommon.2,12,13 Spiegel et al.14 published a series of schwannomas of lower extremity and only 11% of them occurred in the foot. Despite the schwannomas can vary in size from a few millimeters to >20 cm, the majority of them are smaller than 5 cm,11 whereas those larger are termed giant schwannomas.15 To the best of our knowledge, as shown in Table 2 only six giant schwannomas of the foot have been reported to date (Table 2). 8-10,15-17

Table 2: Case reports describing giant schwannomas of the foot
Article Year Localization Size (cm) Bone invasion Local recurrence
Torossian et al.8 2001 Heel 7.5 × 5.5 × 5 No No
Pasternack et al.10 2005 Dorsal aspect of the foot 8 × 4.5 × 2.5 No No
Mangrulkar et al.9 2007 Medial aspect of ankle and hindfoot 14 × 5 × 8 No Yes
Ansari et al.16 2014 Dorsomedial aspect of the foot 7 × 6 Yes No
Flores Santos et al.3 2014 Lateral and plantar aspects of the foot 7 × 2.5 × 3 Yes No
Wang et al.17 2016 Dorsal aspect of the foot Not available Yes No
Francesco et al.18 2016 Medial and plantar aspects of the foot 12 × 8 × 5 No No
Current Study 2019 Dorsomedial aspect of the foot 6.1 × 2.4 × 3.5 No No

Three previous case reports15-17 described giant schwannomas of the foot with a diffuse bone invasion. Whether these osseous schwannomas originated from bone or invaded the bone from elsewhere is a matter of debate. The latter notion however raises a suspicion of malignancy. Malignant transformation of a solitary schwannoma is extremely rare. The overall recurrence rate accounts for <5% of schwannomas in the available literature and seems to be prevented through a complete excision.18,19 The multinodular schwannoma reported by Mangrulkar et al.9 was characterized by a local recurrence 9 months post-op. The case reported by Torossian8 et al. had a recurrence 10 years post-op and was managed by wide excision and a medial plantar flap was used to repair the heel.

Ly reported a solitary schwannoma of the foot but the size of the schwannoma was 1.5 × 2 cm.7 The clinico-radiological findings in this case were suggestive of a ganglionic cyst. It was only on histopathological evaluation that it was found to be a schwannoma.

The diagnosis of schwannoma of the lower extremity is sometimes delayed if the primary complaint is pain and not swelling. This is because the treating physicians consider it to be sciatica. When evaluating a painful mass or an atypical pain in the lower extremity, the clinician should have a high index of suspicion for schwannoma.14 Schwannomas are soft tissue tumors with an unclear cause, although there is a recognized link with von Recklinghausen’s disease (neurofibromatosis type I).20,21 Patients with this condition typically have multiple lesions. Neurofibromas and schwannomas are also the closest differentials for benign peripheral nerve sheath tumors. The distinction between the two is made in MRI evaluation in clinical practice. Neurofibromas typically demonstrate, a “target sign” (low signal intensity in the center and higher signal intensity over the periphery) on T2 scans. The ultimate diagnosis however depends upon the histopathological evaluation.

Classically schwannomas have well-demarcated fibrous capsules and the current case was no exception. This is why we were able to carry out a meticulous en bloc excision. A further procedural alternative of foot amputation was not proposed considering the histological benignity of the schwannoma. Schwannomas may have some degree of cellular atypia, however, this does not always indicate malignancy.2 Immunohistochemistry often shows that these tumors are reactive to S-100 antibodies and negative for other antibodies.22,24

To summarize, it is extremely unusual to see giant schwannomas in feet.2 Schwannomas seldom grow to a large size, particularly in restricted regions like the hands and feet. MRI provides us with a “gold standard” for imaging.2 A complete excision of the schwannoma minimizes its probability of recurrence regardless of its size.

CONCLUSION

The authors have presented two cases of giant schwannoma of the foot in young men, who presented to the clinic with an indolently growing swelling of the foot. Giant schwannomas of the foot are rarely reported and are quite unusual. The authors aim to increase awareness of schwannoma and its clinical presentation by reporting this infrequently encountered condition.

ORCID

Ankit Khurana https://orcid.org/0000-0001-8397-6903

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