Rare case of Ewing's Sarcoma Presenting in the Third Metatarsal: a report

Wayne, Michigan:

Case Report: A 21-year-old female presented to the emergency room with a chief complaint of right foot pain after sustaining a minor injury.

Radiographs of her right foot were taken revealing an incidental cystic lesion in the third metatarsal diaphysis.

The radiographic impression favored an enchondroma with cortical breakthrough and secondary reaction. Other differential diagnoses were considered including osteomyelitis, aneurysmal bone cyst, chondromyxoid fibroma, giant cell tumor, osteo sarcoma, lymphoma, chondrosarcoma, and Ewing's sarcoma.

The radiologist recommended appropriate clinical correlation and further evaluation with follow-up on a nonemergent outpatient basis. The patient was referred to a podiatrist who she saw the succeeding day who recommended monitoring the lesion for any changes.

The patient followed up subsequently with her primary care physician who discovered an increased white blood cell count, decreased iron serum and decreased total iron binding capacity. Her primary care physician then referred her to the author's specialty clinic for a second opinion.

On initial presentation, the patient complained of pain to her right foot but denied any constitutional symptoms including fever, chills, nausea, vomiting, weight loss or loss of appetite. On physical examination, it was noted that she had moderate nonpitting edema and increased skin temperature to the dorsal aspect of her right midfoot with pain on palpation to the level of the third metatarsal diaphysis.

Radiographs consisting of three views of the patient's right foot revealed a fusiform osseous lesion in the third metatarsal distal diaphysis and metaphysis that was 2.7 centimeters in length. The lesion demonstrated a mottled, permeative appearance with ill-defined osseous periosteal reaction.

After reviewing the patient's history, physical examination, radiographic impression and laboratory results from her primary care physician, a timely surgical intervention was warranted due to a likely underlying ominous process.

The patient was boarded for surgical excision and curettage of the right third metatarsal cystic lesion with insertion of allogenic bone graft, biopsy, and culture. A closed image-guided needle biopsy was not considered due to concern for loss of cortical bone and need for a bone graft for stability.

The patient was taken into the operating room where, under local anesthesia with sedation, an open biopsy of the right third metatarsal was performed. Intraoperatively, the third metatarsal dorsal cortex was noted to have disintegrated and the scalpel was easily passed through the remaining dorsal metatarsal shaft while the plantar cortex remained intact. The medullary bone was observed to be gray in color with significant gray drainage. The fluid was cultured and sent to microbiology. Using a sagittal saw and curette, the bone tumor was excised. Half of the bone specimen was sent to microbiology and the other half of the sample was sent to pathology. Following adequate bone resection, the remaining medullary cavity was swabbed with 89% phenol. Bone putty and an allogenic cortical cancellous strut were then placed into the medullary canal to fill the osseous void. The surgical site was then flushed with antibiotic solution, the incision was closed and a silastic drain was placed.

Postoperatively, the patient was immobilized and instructed to remain non-weightbearing. Following the surgical procedure, microbiology determined that bone and culture results were negative for any bacterial growth. Initial pathology results showed no evidence of osteomyelitis and the diagnosis was coined "reactive woven bone." The pathologist had a high suspicion for previous fracture due to multiple areas of fibrous tissue and a large number of osteocytes found within the trabecular bone. With concern for possible malignancy, additional opinions were requested and further histological slides were created and evaluated.

After further investigation, the slides revealed multiple clusters of small round blue cells with a high nuclear to cytoplasmic ratio. A large number of immunohistochemical staining was then performed to identify these small round blue cells. The cells stained strongly positive for CD99, a membranous protein found in certain soft tissue tumors including Ewing's Sarcoma, synovial sarcoma and low grade fibromyxoid sarcoma. Fluorescent in-situ hybridization studies were also performed which were positive for EWSR1 gene rearrangement and this patient was diagnosed with Ewing's Sarcoma.

Once the conclusive diagnosis was confirmed, the patient was referred to an orthopedic oncologist. After a bone scan and chest computed tomography scan, oncology determined there was no evidence of metastatic disease. The patient was then referred to reproductive endocrinology where she underwent fertility preservation. After further follow up with a sarcoma clinic and recommendations from a sarcoma tumor board, the patient underwent 12 weeks of chemotherapy.

Her right foot was reimaged at this time and showed no evidence of recurrence of the bone tumor. The patient then followed up her chemotherapy treatment with five weeks of radiation therapy. At her 1-year follow-up visit, radiographs of the right foot were taken and revealed consolidation of the cortical cancellous graft with no evidence for recurrence of the Ewing's Sarcoma. The patient denied any pain to the right foot and has been ambulating in normal shoe gear. Currently, a year and a half following surgical resection, this patient continues to remain in remission with no evidence of metastasis and no recurrence of the third metatarsal neoplasm.

The authors concluded that - Ewing's sarcoma family of tumors remains rare and aggressive malignant neoplasms that can quickly metastasize, dramatically affecting overall survival. With the rapidly progressive nature of the tumor, a thorough and timely workup is important. In this case study, clinical suspicion of an underlying ominous process led to immediate surgical excision and curettage of the tumor with biopsy and insertion of allogenic bone graft.

Level of Clinical Evidence: 4

Keywords: bone tumor, cyst, EFT, malignancy, metatarsal cyst, metatarsal tumor, PNET

Further reading:

A Rare Presentation of Ewing's Sarcoma Presenting in the Third Metatarsal

Marissa Mogavero, Hannah Khlopas, Lawrence M. Fallat.

The Journal of Foot & Ankle Surgery 61 (2022) 421−425

https://doi.org/10.1053/j.jfas.2021.09.010