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Pseudomyogenic hemangioendothelioma (PMHE) is a rare vascular neoplasm with an intermediate to low-grade malignant potential. Only 5% of PMHEs occur in the head and neck. This tumor exhibits different histological patterns and mimics other vascular tumors, myoid tumors, or carcinomas. The distinction between these tumors can be a very challenging situation for pathologists. In this article, we report the first case, to our knowledge, of PMHE arising in the maxillary sinus, to highlight this uncommon entity and discuss differential diagnoses.

The term \"hemangioendothelioma\" is used for endothelial neoplasms of intermediate malignancy and describes a group of rare neoplasms having biologic behavior falling in between that of the benign hemangiomas and fully malignant angiosarcomas. The hemangioendotheliomas fall into several specific, clinicopathologically and genetically distinct entities, specifically epithelioid hemangioendothelioma, kaposiform hemangioendothelioma, papillary intralymphatic angioendothelioma and retiform hemangioendothelioma (hobnailed hemangioendothelioma), pseudomyogenic hemangioendothelioma, composite hemangioendothelioma, and YAP1::TFE3-fused hemangioendothelioma. The clinical, morphologic, immunohistochemical, and genetic features, and the differential diagnosis of each of these rare entities are discussed in this review.

Pseudomyogenic hemangioendothelioma (PMHE), a rare vascular neoplasm, was first described in 1992 asa fibroma-like variant of epithelioid sarcoma, and would be termed as epithelioid sarcoma-like hemangioendothelioma a decade later due to its significant histologic overlap with epithelioid sarcoma and diffuse cytokeratin expression. PHME is currently defined as a distinct, potentially intermediate malignant, rarely metastasizing neoplasm with vascular/endothelial differentiation. It is characterized by young age (typically less than 40 years old), extremity location (approximately ~80%), and t(7:19) SERPINE1::FOSB fusion as the most common molecular alteration. Herein, we report a case of a 59-year-old male presenting with multifocal lesions, including in the right temporalis muscle, right frontoparietal calvarium, right pterygoid muscles, and right mandibular condyle. Histologic examination of the right temporal lesion revealed a multinodular biphasic lesion composed of sheets and fascicles of elongated spindle and epithelioid cells infiltrating into the adjacent skeletal muscle. Admixed abundant neutrophilic infiltration is noted; however, areas of necrosis, increased mitosis, nuclear atypia, or rhabdomyoblast-like cells are absent. Immunohistochemical (IHC) staining showed that the tumor cells were diffusely and strongly positive for FOSB, pan-cytokeratin (AE1/AE3), CD31, and ERG. Molecular testing demonstrated a t(9:19) EGFL7::FOSB fusion mRNA. This constellation of morphological, IHC and molecular findings was consistent with a diagnosis of PMHE. This is the first reported case of multifocal PMHE with EGFL7::FOSB fusion in the head and neck area of a patient aged more than 50 years old. Since the differential diagnoses for PMHE includes high-grade malignancies with aggressive clinical behavior, coupled with the rare reports of PMHE in the head and neck region, awareness of this tumor in the head and neck region will avoid the misdiagnosis and overtreatment of this entity.

Osseous vascular anomalies can be characterized as vascular tumors or malformations. Classification is vital for prognosis and treatment. Much remains unknown about conditions such as Gorham-Stout disease. Treatments target the proposed genetic pathways such as PI3KCA/AKT/mTOR pathway.

Epithelioid and spindle cell sarcomas with NR1D1::MAML1/2 gene fusions are rare and emerging entities. Only six cases of NR1D1-rearranged mesenchymal tumors have previously been reported in the literature; they are often characterized by an epithelioid morphology, at least focal pseudogland formation, prominent cytoplasmic vacuoles, and focal to diffuse immunohistochemical expression of keratin. We herein report the first case of an NR1D1::MAML1 epithelioid and spindle cell sarcoma with dual immunohistochemical expression of ERG and FOSB, mimicking a pseudomyogenic hemangioendothelioma (PHE) on core biopsy. The sarcoma arose in the left forearm of a 64-year-old man. Initial biopsy showed a mesenchymal neoplasm composed of epithelioid and spindle cells dispersed in myxoid stroma with scattered stromal neutrophils. The morphologic features, combined with the dual immunohistochemical expression of ERG and FOSB, initially mimicked PHE, representing an important potential diagnostic pitfall. The patient subsequently underwent a radical resection, which showed a much more diffuse epithelioid appearance with nested architecture and pseudogland formation. Next-generation sequencing was performed on the resection specimen, which revealed an NR1D1::MAML1 gene fusion, confirming the final diagnosis. Given the fully malignant potential of this tumor, knowledge and recognition of this rare entity are essential to ensure proper management, prevent misdiagnosis, and further characterize the clinical course of this emerging entity. Comprehensive molecular testing can help to identify these rare tumors and exclude the possibility of epithelioid mimics, including PHE.

OBJECTIVE: Pseudomyogenic hemangioendothelioma (PHE) is a rare intermediate hemangioendothelioma. This article aims to study the clinicopathological features of PHE.
METHODS: We collected the clinicopathological features of 10 new PHE, and examined their molecular pathological features by fluorescence in situ hybridization. In addition, we summarized and analyzed the pathological data of 189 reported cases.
RESULTS: The case group consisted of six men and four women aged 12-83 years (median: 41 years). Five instances occurred in the limbs, three in the head and neck, and two in the trunk. Tumor tissues were composed of spindle cells and round or polygonal epithelioid cells, which were either arranged in sheets or interwoven, along with areas of transitional morphology. Scattered or patchy stromal neutrophil infiltration was observed. Tumor cells had abundant cytoplasm, and some contained vacuoles. The nuclei had mild to moderate atypia, with visible nucleoli, and mitosis was rare. PHE tissues diffusely expressed CD31 and ERG, but not CD34, Desmin, SOX-10, HHV8 or S100, while some samples expressed CKpan, FLI-1 and EMA. INI-1 stain is retained. The proliferation index of Ki-67 is 10-35%. Seven samples were detected by fluorescence in situ hybridization, six of which had breakages in FosB proto-oncogene (AP-1 transcription factor subunit). Two patients experienced recurrence; however, no metastasis or death occurred.
CONCLUSIONS: PHE is a rare soft tissue vascular tumor, which has biologically borderline malignant potential, local recurrence, little metastasis, and good overall survival and prognosis. Immunomarkers and molecular detection are valuable for diagnosis.

Pseudomyogenic hemangioendothelioma (PMH), also known as epithelioid sarcoma-like hemangioendothelioma, is a rare epithelioid vascular neoplasm predominantly affecting young adult males at an average age of approximately 30 years. This tumor is rare; therefore, detailed information regarding this tumor is still lacking. Here, we report a case of a man in his 20s presenting with left foot pain for about one year. Imaging showed a 2-cm ovoid, cortically based lesion with a lytic defect of the cortex at the fifth metatarsal proximal shaft. Histologically, the lesion presented as an infiltrating proliferation of distinctly myoid-appearing spindled cells with eosinophilic cytoplasm and mildly atypical vesicular nuclei. Scant mitoses were identified with no areas of necrosis. Tumor cells exhibited strong, diffuse cytokeratin expression as well as CD31 and ERG. CD34 was positive in a few tumor cells, and integrase interactor 1 (INI1) retained nuclear expression. No reactivity for S100, desmin, smooth muscle actin (SMA), epithelial membrane antigen (EMA), and CD1a was present. Over half of the patients with PMH develop multifocal lesions, often involving several tissue planes; however, distant metastasis is very infrequent. This patient underwent curettage and internal fixation of the left fifth metatarsal and had no evidence of recurrence or distant metastasis after seven years of follow-up. Our case contributes to the growing knowledge of PMH and sheds light on the prognosis of these lesions.

Pseudomyogenic hemangioendothelioma (PMH) is a rare tumor of vascular origin with intermediate malignant potential which commonly presents as a subcutaneous and soft-tissue mass with or without concurrent bone involvement. However, PMH presenting as primary multifocal bone lesions is rare. Histomorphologically, it mimicks other epithelioid tumors and cytokeratin expression in PMH can prompt an erroneous diagnosis of metastatic carcinoma, especially in an elderly patient. Diligent histopathological examination and judicious immunohistochemistry panel can guide to the correct diagnosis. Due to its rarity, the optimal therapeutic strategy has not been established till date. We present a rare case of PMH of primary bone with multifocal bony disease in a 23-year-old male who presented with severe bone pains. The patient has been managed with four weekly denosumab, and the disease is stable with symptomatic relief after 6 months.