20.500.12556/RUL-169590 Diagnosis of pediatric myositis ossificans based on cytomorphology and molecular analysis from FNAB sample a case report Myositis ossificans (MO) is a benign soft tissue lesion, characterized by ectopic ossification due to inappropriate fibroblast differentiation, most commonly affecting skeletal muscles. It often occurs in young adults after muscle trauma, predominantly in male patients and very rarely in children. We describe the case of a previously healthy 3-year-old boy who developed a lesion in his deltoid muscle after vaccination against tick-borne encephalitis. During an MRI scan, performed under general anesthesia, fine needle aspiration biopsy (FNAB) and core needle biopsy (CNB) were performed. While the CNB sample resulted in a non-diagnostic finding, the FNAB sample showed cytomorphology consistent with the diagnosis of MO. A molecular analysis performed on the FNAB sample confirmed the presence of COL1A1::USP6 fusion, which is considered diagnostic for MO in the appropriate clinical context. The boy was then referred to the orthopedic surgeon. Extracorporeal shock-wave therapy was chosen as the first-line treatment, but as it was too painful, the lesion was surgically removed, and histopathologic evaluation confirmed the diagnosis. Although rare in children, the diagnosis of MO should be considered in soft tissue lesions after trauma. We present the first pediatric case of MO diagnosed by FNAB and propose that FNAB, as a minimally invasive diagnostic procedure, is a suitable diagnostic approach, especially when molecular testing is available to confirm the diagnosis. USP6 gene case report pediatric diagnosis myositis ossificans pediatrics diagnostic techniques and procedures gene rearrangement molecular pathology fine-needle biopsy large-core needle biopsy core needle biopsy fine-needle aspiration biopsy USP6 gene rearrangements true false true Angleški jezik Ni določen Članek v reviji 2025-06-05 10:20:58 2025-06-05 10:21:00 2025-06-06 04:42:47 0000-00-00 00:00:00 2025 0 0 Str. E138-E143 iss. 7 Vol. 53 2025 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 616-053.2 1097-0339 10.1002/dc.25477 234631171 Diagnostic_Cytopathology_-_2025_-_Ledinek_-_Diagnosis_of_Pediatric_Myositis_Ossificans_Based_on_.pdf Diagnostic_Cytopathology_-_2025_-_Ledinek_-_Diagnosis_of_Pediatric_Myositis_Ossificans_Based_on_.pdf 1 CB5FAA764C59418952196FD7E20AB5E6 e1120f2cadf7d7d8ed8a47b2f1ec8394437614d72f6b5128f4b99b14b36669a8 82961ad5-41e5-11f0-b232-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=211082 https://onlinelibrary.wiley.com/doi/10.1002/dc.25477 1 b223b032-41e4-11f0-b232-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=211079 Medicinska fakulteta 0 0 0