PMC10167840_01
(A) Magnetic resonance imaging (MRI) with gadolinium showing a large malignant peripheral nerve sheath tumor (13x8x7cm) of the median nerve at the level of the forearm. The blue arrows show the median nerve proximal and distal to the tumor. The nerve appears enlarged due to the tumor growing in its context. The white arrow shows the tumor. (B) Postoperative MRI with gadolinium at 30 days postoperatively and every 6 months thereafter documented absence of tumor recurrence or remnants. The red arrow shows postoperative integrity of the median nerve.
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A gadolinium-enhanced MRI showed a large tumor (13 x 8 x 7 cm) arising from the median nerve at the level of the forearm ( Figure 1 ). Serial MRI scans of the forearm with Gadolinium and whole-body CT scan with contrast enhancement at 30 days, 6 months, 1 year, and 18 months postoperatively documented no tumor recurrence, remnants, or metastases ( Figure 1 ). The patient timeline is depicted in  Supplementary Figure 1 .
Microsurgical resection of the tumor was accomplished, and the lesion was removed enbloc: (A) The main trunk of the median nerve is seen running over the tumor surface. (B) Gross appearance of the tumor after resection, placed next to a ruler for scale.
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The patient underwent microsurgical en-bloc tumor resection ( Figure 2 ).
Hematoxylin and eosin-stained sections illustrating the main morphological findings: (A) On low power (10x magnification), classic marbled appearance due to alternating hypocellular and hypercellular areas with perivascular distribution of neoplastic cells is seen. (B) Hypercellular areas of the neoplasm consisting of uniform spindle cells with hyperchromatic, thin, and wavy nuclei are visible. (C) Nuclear atypia and numerous mitotic figures are easily identifiable. (D) Infiltration of the surrounding skeletal muscle is seen.
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Nuclear atypia, numerous mitotic figures, and surrounding skeletal muscle infiltration were observed ( Figure 3 ).
(A-C) A customized immobilization system was created by carving out foamed polyethylene. The patient gripped a cylindrical handle placed at the distal end for increased stability. (B, C) Four reflective body markers placed on the volar surface of the forearm were monitored by two ceiling-mounted infrared cameras for any intra-fraction target motion. (D) Satisfactory cosmetic result at the 1-year follow-up.
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The tumor bed was irradiated with a total dose of 70 Gy in fractions of 2 Gy/day under ExacTrac image guidance as described by Ferini et al. ( Figure 4 ).