Figure it out fridays
A 52-year-old man presented with a huge and firm mass in the posterior right lateral area of the neck with associated restriction of movement. The patient had background of a self-inflicted injury with a knife 4 years prior. He had no other significant medical history. The magnetic resonance imaging (MRI) showed the presence of a subcutaneous mass measuring 13 × 14 × 22 cm in the right posterior lateral area of the neck extending into the posterior thoracic wall. The images were hypointense in T1-weighted images and hyperintense in T2-weighted images. Furthermore, the T1-weighted images showed significant enhancement of the mass and highlighted a central necrotic area Fine- needle aspiration was performed. The mass was interpreted as a spindle-shaped cell tumor without evidence of atypia, consistent with fibromatosis, and negative staining for EMA, MUC4, and S100.
Following discussion by the multidisciplinary oncological group surgical treatment was elected. In the pathology examination, the lesion comprised spindle-shaped cells arranged in long fascicles.
What is the most likely diagnosis?