Musculoskeletal systemCase Type
Muhammad Hussain Mir, Shashank Jagata, Jalal Moradzadeh, Anique Ahmed Choudhary, Ahmed EmiraPatient
65 years, male
A 65-year-old male presented with worsening swelling and pain on the left ankle following trauma 6 weeks ago. He reported no weight loss, fever or any altered neurological symptoms. White blood cell count was 7.6 x 109/L, C-reactive P was 8.1 mg/L, and urate 384 mcmol/L.
X- ray of left ankle showed a lytic lesion centred at the left medial malleolus exhibiting geographic and moth-eaten ill-defined pattern osteolysis with associated with soft tissue component showing no calcifications. (Figure a).
Subsequent MRI of left lower limb showed a large homogenously enhancing mass measuring approximately 47X62X55mm, with marked destruction of the medial malleolus (Figure b) extending into the medial gutter of the tibiotalar joint (Figure c). Further, similarly enhancing soft tissue lesions were seen within the soleus muscle belly and in the peroneal muscles at the proximal to mid fibula level. These lesions exhibit similar imaging pattern. No cortical destruction was seen of the shafts of the tibia or fibula. (Figure d) but non-specific marrow oedema with an increase in the signal at the mid-lower fibular diaphysis was observed likely to be reactive. (Figure e)
Subsequent Ultrasound-guided fine-needle biopsy from the lesion based at the medial malleolus at tertiary centre revealed a high-graded spindle sarcoma (grade 3) favouring a Malignant Peripheral Nerve Sheath Tumour.
Soft tissue tumours bone metastasis is usually observed as lytic lesion in more than 80 % of cases Soft tissue tumours such as angiosarcoma, dedifferentiated liposarcoma and alveolar soft part sarcoma depicts similar kind of lytic bone invasion.
A sarcoma is deemed a malignant peripheral sheath tumour (MPNST)when it originates from a pre-existing benign nerve sheath tumour and demonstrates Schwann cell differentiation in histopathological tests, stemming from the peripheral nerve . MPNST rarely occur denovo and usually (more than half) arise in patients with predisposing conditions like Neurofibromatosis type 1 (NF1), caused by germline loss of function (LOF) of one copy of the tumour suppressor gene NF1. On rare occasions it cal also occur sporadically or after radiation exposure but the overall incidence of this is lower as compared to association with Neurofibromatosis type 1. 
MPNST are histologically easily recognized as malignant tumours and has wide-ranging differentials from other spindle-shaped malignancies such as synovial sarcoma, fibrosarcoma, leiomyosarcoma, metastatic melanoma, and certain benign and reactive spindle cell lesions such as solitary fibrous tumour and nodular fasciitis. There are many variants of the MPNST including epithelioid, divergent and perineural. . MPNST grade three spindle cell sarcoma tend to grow and spread quickly if they are near lymph nodes . In situations where the sarcoma is yet to spread to the lymph nodes, the risk of spreading it to other distant sites is exceptionally high . Spindle cell sarcomas also tend to grow back in the same area after being removed; it is necessary to handle them appropriately and deal with them efficiently 
Therefore, the most applicable treatment is surgical excision of the sarcoma including lymph nodes However, before the surgery, neoadjuvant chemotherapy is usually administered for eight weeks . The purpose of neoadjuvant chemotherapy is to shrink the principal tumour and kill any other cancer cells that may have spread to other body parts. Following the successful removal of the spindle cell sarcoma through surgery, samples are usually sent for histopathology and microscopy to determine whether sarcoma has been excised completely. Additionally, microscopic examination assists in determining the quantity of the tumour that has been killed during neoadjuvant chemotherapy . The patient then undergoes adjuvant chemotherapy for a period of 16 to 24 weeks. Adjuvant chemotherapy lowers the risk of the sarcoma re-occurring, ensuring the patient is safe from future incidences of sarcoma. Follow-up care is critical following the completion of the adjuvant chemotherapy session. The patient must attend frequent outpatient check-ups for clinical health assessments to detect any late effects of the cancer treatment performed .
The above patient was referred to the sarcoma unit at a tertiary care centre where MDT discussion following biopsy advised further investigations and a contrast-enhanced CAP which later revealed bilateral renal masses and left lower lung mass with left hilar adenopathy, considering already aggressive metastasis with poor prognosis he was later followed up by MDT at tertiary centre for considering palliative management options and no more actions were taken regarding histopathology diagnosis for the chest or renal masses (as no change to the management decision expected). However, RCC as a secondary primary tumour was still considered as a differential for the renal masses.
In conclusion, it is important to realise that patients might not come with any obvious signs or symptoms apart from soft tissue swelling. Therefore, suspicious incidental findings of soft tissue swelling with lytic bone involvement picked up on radiographs should be followed through with appropriate further imaging like MRI.
Furthermore, biopsy to determine or confirm diagnosis histopathologically and referral to a specialised MDT is warranted in all such cases.
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