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Abstract Background Pseudosarcomatous myofibroblastic proliferation is a rare proliferative lesion of the submucosal stroma characterized by myofibroblast proliferation and inflammatory cell infiltration, and is mainly reported in the urinary system. Case presentation We report a 65-year-old male who was referred to our emergency room with right-side iliac fossa pain. The pain gradually worsened for approximately 2 months, and rebound tenderness was positive. Blood examination showed severe inflammatory findings, and enhanced computed tomography revealed a heterogeneous contrast-enhancing mass lesion measured to be 55 × 50 mm in size at the lower right abdomen. Based on these results, the patient was diagnosed with appendicitis with an abdominal abscess. As the inflammation was severe, we drained the abscess before performing surgery. Approximately 1 month after the abscess diminished, interval appendectomy was performed. Macroscopic findings of the resected specimen showed a perforated diverticulum of the appendix and a small adjacent nodule measured to be 14 mm in size. Histopathological examination with hematoxylin and eosin staining revealed that the nodule consisted of fibroblast proliferation and inflammatory cell infiltration. Furthermore, immunohistochemical examination showed positive for smooth muscle actin and desmin and negative for S-100, c-kit, and anaplastic lymphoma kinase. Based on these histopathological results, we diagnosed the nodule as an unusual case of a pseudosarcomatous myofibroblastic proliferation associated with perforation of the diverticulum of the appendix. Conclusion Herein, we report a rare case of a pseudosarcomatous myofibroblastic proliferation that occurred in the appendix with diverticulitis.

Reactive spindle cell nodules (RSCNs) that occur after fine needle aspiration (FNA) are commonly documented in the literature. They are benign proliferation of spindle cells with some mitotic figures and nuclear pleomorphism that arise after tissue injuries like FNA. These lesions are non-capsulated and surrounded by parenchyma of organ tissue. Although RSCNs after FNA can occur in various organs of the body, there is a lack of well-established studies describing their presence in the pancreas. We present a case of a 74-year-old female treated with pancreatectomy for intraductal papillary mucinous neoplasm (IPMN), and RSCNs were found incidentally during post-surgery microscopic evaluation. This lesion showed similar characteristic microscopic features of the RSCNs found at different anatomical sites. To the best of our knowledge, this may be the first case of RSCNs after FNA into the pancreatic. This case expands the diagnostic framework of pancreatic spindle cell tumors., Competing Interests: Human subjects: Consent for treatment and open access publication was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Akbari et al.)

Aims: Pseudosarcomatous myofibroblastic proliferations (PSMPs) of the urinary bladder are diagnostically challenging. Diagnostic difficulties are mainly due to frequent cytokeratin expression, variable ALK expression and worrisome morphological features suggestive of malignancy. Conversely, sarcomatoid urothelial carcinoma (UC) may show bland inflammatory myofibroblastic tumour (IMT)‐like morphology. TERT promoter mutations are characteristic events in urothelial cancers, but have not been studied in PSMPs. Methods and results: We compared histomorphological and immunohistochemical features and TERT promoter status in 16 PSMPs and 18 sarcomatoid UC. In a subset of PSMPs, RNA sequencing was performed. At least focal IMT‐like morphology was seen in nine of 17 sarcomatoid UC. Atypical mitoses, differentiated urothelial component and heterologous elements were the most reliable distinguishing histomorphological features of sarcomatoid UC, if present. A panel of immunohistochemistry (IHC) including ALK (clone D5F3), p53 pattern, p63 and GATA3 reliably distinguished PSMP from sarcomatoid UC. GATA3 (P = 0.001) and p53 patterns (mutant versus wild‐type; P < 0.001) were differentially expressed between PSMPs and sarcomatoid UC. Diffuse pancytokeratin staining was significantly associated with PSMPs (10 of 13) compared to four of 14 sarcomatoid UCs (P = 0.012). TERT promoter mutations were found in 17 of 18 sarcomatoid UC versus none of 16 PSMPs (P < 0.001). RNA sequencing revealed ALK genetic rearrangements in one of two ALK‐positive and one of 10 ALK‐negative PSMPs, which revealed a novel FN1/RET gene fusion. Conclusion: Careful histomorphological analysis and differential IHC reliably distinguish the majority of PSMPs and sarcomatoid UC. In equivocal cases, TERT promoter mutation analysis and/or detection of ALK expression/rearrangements are valuable additional diagnostic adjuncts, strongly supporting sarcomatoid UC and PSMP, respectively. [ABSTRACT FROM AUTHOR]

Background: Pseudosarcomatous myofibroblastic proliferation is a rare proliferative lesion of the submucosal stroma characterized by myofibroblast proliferation and inflammatory cell infiltration, and is mainly reported in the urinary system. Case presentation: We report a 65-year-old male who was referred to our emergency room with right-side iliac fossa pain. The pain gradually worsened for approximately 2 months, and rebound tenderness was positive. Blood examination showed severe inflammatory findings, and enhanced computed tomography revealed a heterogeneous contrast-enhancing mass lesion measured to be 55 × 50 mm in size at the lower right abdomen. Based on these results, the patient was diagnosed with appendicitis with an abdominal abscess. As the inflammation was severe, we drained the abscess before performing surgery. Approximately 1 month after the abscess diminished, interval appendectomy was performed. Macroscopic findings of the resected specimen showed a perforated diverticulum of the appendix and a small adjacent nodule measured to be 14 mm in size. Histopathological examination with hematoxylin and eosin staining revealed that the nodule consisted of fibroblast proliferation and inflammatory cell infiltration. Furthermore, immunohistochemical examination showed positive for smooth muscle actin and desmin and negative for S-100, c-kit, and anaplastic lymphoma kinase. Based on these histopathological results, we diagnosed the nodule as an unusual case of a pseudosarcomatous myofibroblastic proliferation associated with perforation of the diverticulum of the appendix. Conclusion: Herein, we report a rare case of a pseudosarcomatous myofibroblastic proliferation that occurred in the appendix with diverticulitis. [ABSTRACT FROM AUTHOR]

Aims: Pseudosarcomatous myofibroblastic proliferations of the genitourinary tract have a debatable relationship with inflammatory myofibroblastic tumour (generally lacking ALK rearrangement); however, they share several overlapping features with nodular fasciitis of soft tissue. As rearrangement of the USP6 gene has been recently recognised as a recurrent alteration in soft tissue nodular fasciitis, and several other alternative gene fusions have been recently recognised in inflammatory myofibroblastic tumour, the aim of this study was to investigate whether USP6, ROS1 or ETV6 rearrangements were present in these lesions (12 cases). Methods and results: Fluorescence in‐situ hybridisation analysis was performed by the use of bacterial artificial chromosome‐derived break‐apart probes against USP6, ROS1, and ETV6. Two cases with adequate genetic material from recent paraffin tissue blocks were also tested by use of a solid tumour gene fusion detection assay via next‐generation sequencing, targeting >50 known genes involved in recurrent fusions. None of the genitourinary pseudosarcomatous myofibroblastic proliferations was found to harbour USP6 (0/12), ROS1 (0/8) or ETV6 (0/7) rearrangements, and no gene fusions were detected in two cases studied by sequencing. Conclusions: Despite overlap in histological and immunohistochemical features between pseudosarcomatous myofibroblastic proliferation and nodular fasciitis, these tumours lack the recently recognised USP6 rearrangements that occur in nodular fasciitis, as well as alternative fusions found in ALK‐negative inflammatory myofibroblastic tumours. At present, this diagnosis remains based primarily on clinical, histological and immunohistochemical features. [ABSTRACT FROM AUTHOR]

Inflammatory myofibroblastic tumors (IMTs), which are rare tumors, exhibit myofibroblastic differentiation, often with anaplastic lymphoma kinase (ALK) gene rearrangements. A subset of IMTs identified in the urinary tract have been shown to harbor a fibronectin 1 (FN1)-ALK gene fusion. In this case report, a case of an IMT with FN1-ALK fusion in the urinary bladder was presented, and its clinicopathological characteristics were reviewed. A 45-year-old female was referred to Chungbuk National University Hospital with gross hematuria. Cystoscopy revealed a solid mass in the bladder. The patient subsequently underwent transurethral resection of the lesion. The mass comprised stellate and spindled myofibroblastic cells that were arranged in loose fascicles, with a myxoid background and a mixed inflammatory infiltrate. Immunohistochemical analysis revealed that the tumor cells were positive for vimentin, cytokeratin AE1/AE3 and ALK, and focal-positive for desmin. Targeted next-generation sequencing was subsequently employed to identify the FN1-ALK fusion. To date, the patient has undergone outpatient follow-up for 18 months, with no signs of tumor recurrence. To conclude, in total, FN1 has been identified as an ALK fusion partner almost exclusively in cases of genitourinary IMTs [13 bladder IMTs (including the present case) and two uterine IMTs]. In the present case, the FN1-ALK fusion was found to involve ALK exon 19 and FN1 exon 23. By contrast, the majority of the other IMTs with an ALK fusion have involved ALK exon 20, whereas ALK fusion involving ALK exon 18 or 19 has been reported only in genitourinary IMTs. Therefore, the FN1-ALK fusion involving ALK exon 18 or 19 may be specific to a subset of IMTs arising in the urinary bladder. [ABSTRACT FROM AUTHOR]

Head and neck lesions composed of spindle cells evoke a differential diagnosis which includes a host of benign and malignant entities. One of the less common spindle cell lesions in this region is the inflammatory myofibroblastic tumor (IMT). Although IMTs were originally regarded as 'pseudotumors', they are now recognized to be true neoplasms. Local recurrence, and, rarely, malignant change have been reported. Currently, the definitive means of diagnosing IMTs is the identification of a rearrangement of the anaplastic lymphoma kinase gene (at chromosome 2p23) by fluorescence in situ hybridization. The histopathologic differential diagnosis includes infectious processes, other fibro-inflammatory lesions, lymphoma, the inflammatory variant of malignant fibrous histiocytoma, and sarcomatoid (spindle cell) carcinoma. Complete surgical excision is the treatment of choice. [ABSTRACT FROM AUTHOR]

Spindle cell lesions of the urinary tract encompass a variety of benign and malignant tumours as well as a group of lesions of controversial nomenclature that is the subject of ongoing debate. This review focuses on our current and evolving understanding of the lesion variably referred to as inflammatory myofibroblastic tumour, pseudosarcomatous myofibroblastic proliferation or inflammatory pseudotumour and the main differential diagnoses of sarcomatoid carcinoma and sarcoma. Other spindle cell lesions of the bladder are described. [ABSTRACT FROM AUTHOR]

Despite the frequent use of fine-needle aspiration, core biopsy and surgery, postoperative spindle cell nodule (PSCN) is a rare pathological complication that may be diagnostically treacherous. Presented herein is the case of a 52-year-old woman who developed a 7 mm mammary nodular lesion 66 days after removal of an area of columnar cell hyperplasia involving cellular and architectural atypia, performed with the Mammotome Breast Biopsy System. The lesion was highly cellular and composed of intersecting fascicles of plump spindle cells with blunt-ended elongated nuclei and nucleoli easily visible. Interspersed mononuclear cells and hemosiderin-laden macrophages were evident. PSCN is a reactive, benign myofibroblastic proliferation. Differential diagnosis includes benign and malignant spindle cell lesions of the breast. Recognition of this reactive lesion will avoid overdiagnosis of spindle cell malignant tumor. Attention to clinicopathological and histological features should result in accurate recognition of this lesion. [ABSTRACT FROM AUTHOR]

Pseudosarcomatous myofibroblastic proliferation (PMP) of the bladder is a rare, benign, and proliferative lesion of the submucosal stroma. We report a 38-year-old female patient who was initially diagnosed with urothelial carcinoma of the urinary bladder under intravenous pyelography. Bladder tumor was resected by the transurethral method, and pathology disclosed a picture compatible with pseudosarcomatous myofibroblastic proliferation. However, local recurrence was found 2 months later, and tumor resection was performed again. The patient has been followed-up at our outpatient department for a year without any evidence of recurrence. [Copyright &y& Elsevier]

We describe 17 cases of distinct benign pseudomalignant mesothelial proliferations, involving the spermatic cord. All cases revealed necrosis. The areas adjacent to the necrotic tissue comprised a cellular spindle cell proliferation with a haphazard arrangement of the myofibroblasts that in many areas revealed transitions into plump oval epithelioid cells and into cells with genuine epithelial appearances arranged in linear cords and often luminized into small microcysts. These epithelial cells formed isolated groups with glandular structures arising on the myofibroblastic background. Glandular structures were often situated deeply in the stroma of the spermatic cords. All cellular elements were strongly positive with AE1/AE3 antibody. All myofibroblasts stained with SM-actin antibody. Ultrastructurally, the spindle cells displayed features of myofibroblasts including actin microfilaments, as did the plump epithelioid cells that, additionally, had desmosomes, and the cords of the epithelial cells including those forming glandular structures had characteristics of mesothelias including the characteristic microvilli. [ABSTRACT FROM AUTHOR]

A pseudosarcomatous myofibroblastic proliferation is an unusual and a rare benign lesion which arises from the bladder submucosal stroma and is easily mistaken for a malignant neoplasm, clinically, radiologically and histologically. By definition, the tumour is composed of a dominant spindle cell proliferation with a variable inflammatory component. These spindle cells are now known to be myofibroblasts and this is the reason for the current designation for this disease. The term 'inflammatory' may not be applicable to all the tumours, since some investigators have demonstrated the presence of chromosomal abnormalities and have documented cases which showed recurrence, thus supporting the theory that at least some of these tumours were true neoplasms. Non-epithelial tumours account for 2-5% of all the primary urinary bladder neoplasms, with the most common types being rhabdomyosarcoma in patients under the age of 10 years and leiomyosarcoma in adults. A pseudosarcomatous myofibroblastic tumour is a nonepithelial lesion that follows a benign indolent course and a conservative management has been reported as the treatment of choice. Herein, we are reporting a case of a pseudosarcomatous myofibroblastic tumour which was mistaken for a sarcoma clinically and radiologically and which was proved as a pseudosarcomatous inflammatory myofibroblastic tumour by histopathology and immunohistochemistry. [ABSTRACT FROM AUTHOR]