case_images: PMC10884780_01
case_images: Clinical image shows a medial parapatellar mass in the right knee (red arrows), keloid scarring from the previous approach (black arrows), with no inflammatory signs adjacent to the mass.
case_images: cureus-0016-00000052739-i01.jpg
case_images: PMC10884780_01_cureus-0016-00000052739-i01.jpg
case_images: FIG1
case_images: The mass was 4 cm long, and the patient reported a notion of curvature on the medial aspect of the right knee (Figure 1).
case_images: X-ray of the right knee (side view (a) and front view (b)) shows no bone damage.
case_images: cureus-0016-00000052739-i02.jpg
case_images: PMC10884780_01_cureus-0016-00000052739-i02.jpg
case_images: FIG2
case_images: X-ray of the knee was normal (Figure 2).
case_images: MRI of the right knee shows an oval tissue mass in the medial soft tissues of the right knee opposite the patella (yellow arrows) with deep and superficial development (orange arrows), containing no hemorrhagic components with heterogeneous enhancement after injection of gadolinium (red arrows) and no osteoligamentous, meniscal, or tendon abnormalities in the knee (green arrows).. MRI, magnetic resonance imaging
case_images: cureus-0016-00000052739-i03.jpg
case_images: PMC10884780_01_cureus-0016-00000052739-i03.jpg
case_images: FIG3
case_images: Magnetic resonance imaging (MRI) of the knee showed a tissue formation in the medial soft tissues of the right knee opposite the patella with deep and superficial development, roughly oval-shaped, intermediate hyposignal in T1, intermediate signal in T2, and discrete diffusion hypersignal, heterogeneously enhancing after injection of Gadolium, not fading on the STIR sequence, no hemorrhagic component, in contact with the medial collateral ligaments, no joint effusion, and no osteoligament, meniscus, or tendon abnormalities in the knee (Figure 3).
case_images: Microscopic examination of the lesion shows diffuse infiltration of the deep dermis by a spindle cell tumor ((a) H&E x40). Tumor cells are spindle-shaped, exhibiting mild to moderate atypia, and surrounded by a fibrous stroma ((b) H&E x400). Immunohistochemical staining demonstrates a strong but limited positivity of tumor cells for both S100 (c) and SOX10 (d).. H&E, hematoxylin and eosin
case_images: cureus-0016-00000052739-i04.jpg
case_images: PMC10884780_01_cureus-0016-00000052739-i04.jpg
case_images: FIG4
case_images: The anatomopathological study revealed a histological and immunohistochemical appearance in favor of a low-grade peripheral nerve sheath tumor with a proliferative index assessed by ki67 of 20% (Figure 4).
case_images: Intraoperative image shows the limits of the skin incision (a) and the mass after resection (b).
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case_images: PMC10884780_01_cureus-0016-00000052739-i05.jpg
case_images: FIG5
case_images: The mass was resected in its entirety while respecting the tendon structures of the knee (Figure 5).