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A 12-year-old, 3 kg spayed female mixed-breed dog was evaluated to assess a 1-year history of intermittent right forelimb lameness that did not have adequate response to nonsteroidal anti-inflammatory drugs. The radiographic study performed under sedation showed multifocal radiolucent areas affecting both the right humerus and scapula with focal soft tissue swelling; a CT scan confirmed the existence of an aggressive and invasive soft tissue mass affecting the scapulohumeral joint. Fine needle aspiration results suggested a low-grade synovial sarcoma and therefore a scapulectomy was performed. The biopsy showed spindle to stellated cells immersed in a basophilic and mucinous (myxoid) matrix with mild to moderate anisocytosis, moderate anisokaryosis, some binucleated cells and sporadic multinucleated cells. These findings are consistent with low-grade synovial myxosarcoma, a not well described synovial neoplasm that can mimic other commonly seen joint tumors or even septic arthritis on radiographs. The purpose of this case report is to describe the first reported synovial myxosarcoma affecting the scapulohumeral joint of a small dog.

Background Primary pulmonary myxoid sarcoma (PPMS) is a rare, low-grade malignant tumor, constituting approximately 0.2% of all lung tumors. Despite its rarity, PPMS possesses distinctive histological features and molecular alterations, notably the presence of EWSR1-CREB1 gene fusion. However, its precise tissue origin remains elusive, posing challenges in clinical diagnosis. Case demonstration A 20-year-old male patient underwent a routine physical examination 6 months prior, revealing a pulmonary mass. Following surgical excision, microscopic evaluation unveiled predominantly short spindle-shaped tumor cells organized in a fascicular, beam-like, or reticular pattern. The stromal matrix exhibited abundant mucin, accompanied by lymphocytic and plasma cell infiltration, with Russell bodies evident in focal areas. Immunophenotypic profiling revealed positive expression of vimentin and epithelial membrane antigen in tumor cells, whereas smooth muscle actin and S-100, among others, were negative. Ki-67 proliferation index was approximately 5%. Subsequent second-generation sequencing identified the characteristic EWSR1-CREB1 gene fusion. The definitive pathological diagnosis established PPMS. The patient underwent no adjuvant chemotherapy or radiotherapy and remained recurrence-free during a 30-month follow-up period. Conclusions We report a rare case of PPMS located within the left lung lobe interlobar fissure, featuring Russell body formation within the tumor stroma, a novel finding in PPMS. Furthermore, the histomorphological characteristics of this case highlight the diagnostic challenge it poses, as it may mimic inflammatory myofibroblastic tumor, extraskeletal myxoid chondrosarcoma, or hemangiopericytoma-like fibrous histiocytoma. Therefore, accurate diagnosis necessitates an integrated approach involving morphological, immunohistochemical, and molecular analyses.

Myxofibrosarcoma is a malignant fibroblastic soft tissue neoplasm containing a variable amount of myxoid stroma that commonly presents as a slow-growing mass in elderly patients. The neoplasm may be superficial or deep to the muscle fascia and characteristically has an infiltrative growth pattern with a dominant or multinodular mass. We describe an unusual case of high-grade myxofibrosarcoma of the wrist and forearm that infiltrated the muscles, tendons, and wrist joint, causing bone erosions. The tumor was mistakenly diagnosed as synovitis and a chronic, erosive, inflammatory process. The diffuse nature, absence of a dominant mass, and radiographic appearance complicated the diagnosis. Although neoplasms of the synovial spaces are rare, this case demonstrates that tumors with a highly infiltrative growth pattern can mimic inflammatory synovitis and that neoplasms should be considered in the differential diagnosis when clinical and laboratory features are discordant with the imaging appearance.

Myxofibrosarcoma is a common sarcoma in the extremities of older people, but is rare in the head and neck region. Here, we report the case of a 42-year-old male patient in whom myxofibrosarcoma generated from the sinus piriformis. Histopathologically, the tumor was characterized by spindle cellular proliferation with moderate cellular density in fibromyxoid stroma. Immunohistochemically, the tumor cells showed positive reactivity for vimentin, Ki-67, smooth muscle actin, and CD34, but negative staining for S-100. Based on these results, the tumor was diagnosed as a low-grade myxofibrosarcoma. Resection of the tumor was performed via a transcervical approach. The patient’s postoperative clinical course was uneventful and no local recurrence or distant metastasis has been found so far. The pathology, clinical characteristics, and treatment of myxofibrosarcoma are also reviewed.

Echocardiography revealed a left atrial tumor in a 59-year-old man with back pain that concurrently worsened with left foot drop and loss of the left ankle reflex soon after admission to our hospital. Magnetic resonance imaging of the spine revealed an epidural tumor extending from Th5 with spinal cord compression. The patient was immediately treated by emergency Th4–5 laminectomy and epidural decompression. One month later, a cardiac tumor excised via the left atrial approach was histopathologically diagnosed as myxosarcoma, and the Th5 tumor was consistent with this finding. This is the first report to describe spinal metastasis of cardiac myxosarcoma.

Primary intracranial myxofibrosarcoma is exceedingly rare, with less than 10 cases published. We present a case of a 23-year-old man with previous history of a primary low grade myxofibrosarcoma of the left parietal-occipital convexity resected in March 1999. He subsequently underwent several interventions for multiple local recurrent disease until March 2004. At that time, complete remission was documented. About 8 years later, in February 2012, the patient was admitted to the emergency room with refractory acute pulmonary oedema. On work up, sustained monomorphic ventricular tachycardia and hyperechoic myocardial mass with invasion of the right ventricular cavity were detected. Electrical cardioversion was unsuccessful and irreversible cardiac arrest followed. The autopsy confirmed multiple bilateral lung metastases, malignant pulmonary embolism and myocardial invasion by the primary tumour, with intracavitary cardiac thrombosis and absence of intracranial disease. To the best of our knowledge, this is the first report of extracranial metastases of this neoplasm.

Extraskeletal myxoid chondrosarcomas (EMC) are extremely rare and are usually located in the deep soft tissues of the lower extremities. Less than 10 cases of intracranial EMC have been reported in the literature, making their management and early diagnosis difficult. We present a new case of intracranial EMC occurring in a 70-year-old woman presenting with a right frontal mass initially assumed to be a brain metastasis from breast adenocarcinoma. The optimal management of these tumours is also discussed. Analysis from the literature suggests that complete resection should be recommended, whenever feasible. Although the high risk for relapse after surgery encourages postoperative treatments, relative resistance to both radiotherapy and chemotherapy characterizes EMC. Future perspectives might include multimodal treatments with highly conformal radiotherapy modalities for dose escalation strategies or use of new molecules. Knowledge of these unusual malignant tumours will be the first step for improving patients’ outcome. Pozaszkieletowy chrzęstniakomięsak śluzowaty to wyjątkowo rzadki guz, który występuje zwykle głęboko w tkankach miękkich kończyn dolnych. Opisano mniej niż 10 przypadków tego guza umiejscowionych śródczaszkowo, co utrudnia wczesne rozpoznanie i leczenie. W pracy przedstawiono nowy przypadek śródczaszkowego chrzęstniakomięsaka śluzowatego u 70-letniej kobiety z guzem okolicy czołowej prawej, traktowanym początkowo jako przerzut gruczolakoraka sutka do mózgu. Omówiono optymalne leczenie tych guzów. Analiza piśmiennictwa wskazuje, że w miarę możliwości powinno się zalecać całkowite wycięcie. Duże ryzyko wznowy po leczeniu chirurgicznym skłania do podejmowania dodatkowego leczenia, ale guz charakteryzuje się względną opornością na radioterapię i chemioterapię. Przyszłe wielorakie metody leczenia mogłyby wykorzystywać radioterapię konformalną w celu zwiększenia dawki promieniowania lub zastosowanie nowych cząsteczek. Wiedza o tych rzadkich nowotworach złośliwych będzie pierwszym krokiem do poprawy wyników leczenia.

A 36-year-old man suffering from exertional dyspnea was admitted to our hospital. An echocardiogram showed a left atrial tumor, which was excised via the left atrial approach. Histological examination of the surgical specimen revealed that it was a myxosarcoma. Twelve months after the surgery, the tumor recurred in the left atrium, and metastatic tumors were found in the right atrium and right ventricle. Surgery was performed once again, but examinations 5 months after the second surgery showed local recurrences and multiple metastases. Although the patient had received chemotherapy, he died 30 months after the first operation.