ECP 2023 Abstracts

S360 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-22-029 Discrimination of bone and cartilage by speed-of-sound K. Miura*, T. Iwashita *Department of Regenerative and Infectious Pathology, Hamamatsu University School of Med, Japan Background & objectives: Scanning acoustic microscopy can assess tissue elasticity because more rigid tissues show higher speed-of-sound (SOS). Bones show variable stiffness in growing ossification, fracture recovery stages, and osteogenic neoplasia. This study evaluates bone and cartilage stiffness to understand the pathological state. Methods: Unstained flat decalcified sections in 10 μm thickness were scanned to plot SOS values of each area on the screen in serial colours. Special resolution was 4.7 μm. Finished SOS images were compared with LM images to analyse the relationship between stiffness and his- tological structure. Adult mouse and human specimens’ cartilages, osteoids, and mineralized bones were compared in various conditions. Results: Virtual SOS images made by plotting SOS values on each location of the section corresponded well to their palpable stiffness and LM images. SOS values (mean ± SD) of cartilages, osteoid, and bones presented 1524.2±35.8, 1632.4 ± 48.6, 1794.4 ± 81.1 m/s, respec- tively. Bone formation from membranes and cartilage were visualized by alteration of SOS values in developing bones, fracture callus, and various bone tumours. Lamellar bones consisting of thick collagen bundles showed multilayer sheets with high SOS values, while woven bones presented a reticulated structure with lower SOS values. Colour images of SOS were changeable to adopt the SOS range within the region of interest. Conclusion: SOS images are comparable with LM ones and corre- spond well to bone and cartilage stiffness to discriminate these states. Numerical values of SOS are relative to bone or cartilage structures to reveal bone formation, fracture recovery, and the metabolic state in sections. SOS images determined woven or lamellar bones. Because unstained sections are free from stain bias and obtained SOS data are objective, SAM can be a scientific tool to evaluate regenerative, meta- bolic, and neoplastic diseases of orthopaedics. E-PS-22-030 Aneurysmal bone cyst-like myositis ossificans of the digit - a rare occurrence S. Naresh Shah* *Apollo hospitals, India Background & objectives: Myositis Ossificans is a self-limited reac- tive process of heterotopic bone formation in soft tissue, which usu- ally follows a trauma. Secondary Aneurysmal bone cyst in soft tissue lesions, a rare occurrence, is believed to be a change associated with hematoma formation. Methods: A 45 year old man presented with swelling in his left ring finger, of one month duration (only history provided at the time) to histopathology department at Apollo hospitals, India. We received an excision biopsy with clinical diagnosis of “osteoma” from remote cen- tre. Radiologically, only roentogram was done which was suggestive of Nora’s lesion. No fluid filled spaces were appreciated. Results: The specimen was received in fragments. Histologically, there were zonation phenomena with spindled myofibroblasts in the centre, surrounded by immature woven bone and mature bone in the periph- ery. In the centre of the lesion cystic blood-filled spaces with septae and surrounding multinucleated giant cells were seen. On persistent perusal, a history of trauma to the finger was obtained. Hence, a diag- nosis of ABC-like MO was made. Conclusion: This is a rare case of ABC-like MO presenting at an unusual site (finger), with only two other such cases in the literature to the best of our knowledge. The history of trauma favoured a diagnosis of ABC-like MO rather than MO-like ABC. USP6 rearrangement by FISH is seen in both ABC and MO and may not help in differentiating between the two entities. E-PS-22-031 Malignant peripheral nerve sheath tumour with perineural dif- ferentiation (malignant perineurioma) E. Pérez Béliz*, L.I. Rojo-Alvarez, I. Abdulkader Nallib, J.M. Came- selle-Teijeiro, M. Piso Neira, F.J. Caneiro Gómez *Clinical University Hospital of Santiago de Compostela, Universidad de Santiago de Compostela and Galician Healthcare Service (SER- GAS), Santiago de Compostela, Spain Background & objectives: Malignant peripheral nerve sheath tumour (MPNST) with perineural differentiation, is a spindle cell sarcoma with positivity for EMA, claudin-1 or GLUT-1, that arises in adults, in extremities or trunk. Here we describe one case illustrating the diag- nostic difficulties encountered. Methods: Histopathological, immunohistochemical and FISH analysis of one case presented in a man of 58 years of age with an axillary mass, adjacent to the brachial plexus, and ipsilateral shoulder pain. Results: First, a needle biopsy was performed, showing a malignant spindle cell neoplasm with scattered pleomorphic cells, necrosis and myxoid stroma. The preliminary immunohistochemical analysis was inconclusive, and a diagnosis of undifferentiated pleomorphic sarcoma was made. The patient received radiotherapy, chemotherapy, and ulte- rior radical surgery. The tumour consisted of a 16 centimetres multi- lobular myxoid mass, with an histological appearance similar to the first biopsy. Tumour cells showed positivity for CD34, EMA, GLUT-1, cytokeratins and focal SMA, and were negative for desmin and MUC4. FISH analysis for FUS showed absence of rearrangements. Hence, a diagnosis of malignant perineurioma was proposed. Conclusion: Malignant perineurioma is an infrequent, neglected vari- ant of MPNST. Given its undifferentiated pleomorphic appearance, such diagnosis can become a challenge, particularly in needle biop- sies. Differential diagnosis must include conventional MPNST and low grade fibromyxoid sarcoma, therefore the relevance of MUC4 stain- ing and FUS rearrangements analysis. Positivity for EMA and CD34, alongside GLUT-1 or claudin-1, should raise suspicion for this tumour. Awareness of this entity, proper sampling, and a standardized immu- nohistochemical panel will lead to an accurate diagnosis of malignant perineurioma. E-PS-22-032 Primary pleuropulmonary synovial sarcoma: a case report with review of the literature D. Proca*, D. Zenezan, J. Yin *Temple University Health System, USA Background & objectives: Primary pleuropulmonary synovial sar- coma (PPSS) is a rare malignant tumour, accounting for 0.1% to 0.5% of all primary lung malignancies. PPSS is associated with a character- istic t(X;18) (p11.2; q11.2) chromosomal translocation. Methods: Our patient is a 24-year-old female who was previously healthy and active. She presented with two weeks of posterior left chest wall pain, dyspnea, and neuralgia of left upper arm. A heterogeneous pleuropulmonary mass in the left lower hemithorax was discovered on Chest CT scan; it measured 10.5 x 8.7 x 8.0 cm and had associated pleural effusion. Results: Biopsy of the mass showed high cellular fascicles of mono- morphic spindle cells with infrequent mitoses and hemangiopericytic vascular pattern. The neoplastic cells were reactive for TLE-1 (indica- tive of synovial sarcoma), vimentin and bcl-2, with focal, non-specific weak staining with desmin, calponin, and CD99. A ki-67 proliferative index was approximately 15%. The tumour was negative for AE1/AE3, CK5/6, CK7, CK20, CK19, EMA, STAT6, myogenin, S100, SOX 10,