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Nodular fasciitis is a rare but benign fibroblastic proliferation that typically presents as a solitary lesion with rapid growth and variable mitotic activity. The lesions usually occur on the extremities and occasionally in the head/neck region. Involvement of the buccal mucosa is extremely rare with only few reports in the literature; in this case report, we describe a 41 year old female who presented with a 6-month history of a stable intraoral lump at the junction of the upper and lower lip. Fine needle aspiration revealed an atypical spindle cell population with plump cells. The surgical excision demonstrated a well circumscribed tan-white firm nodule. Histologic examination revealed a spindle cell proliferation that grew in short, intersecting fascicles with focal storiform architecture. The lesion had a pushing border that was not overtly infiltrative and the stroma contained focal myxoid changes giving a "tissue culture" appearance to the cells. Immunohistochemical testing showed the tumor cells were vimentin (+), SMA (+), weakly Calponin (+), and desmin (-), cytokeratin (-), AE1/AE3 (-), S100 (-), ALK (-), STAT6 (-), and beta-catenin (-). Fluorescence in-situ hybridization (FISH) revealed a USP6 gene rearrangement with an atypical probe pattern. Next generation sequencing identified a novel SPTAN1::USP6 fusion gene confirming the diagnosis of buccal nodular fasciitis. Identification of the characteristic histologic features and USP6 gene rearrangements helped support the diagnosis. A review of the literature identified 25 cases of nodular fasciitis involving the buccal mucosa. The occurrence of this tumor in an unusual location may pose difficulties for diagnosis., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Case: We report a case of intraneural nodular fasciitis in the forearm initially suspected as a schwannoma, emphasizing the importance of accurate diagnosis. A 40-year-old woman presented with mass on the lateral aspect of her right forearm and radial neuropathy symptoms for 2 months. An excisional biopsy and histopathological examination confirmed nodular fasciitis. Postoperative evaluation at 4.5 years found no pain, paralysis, or recurrence., Conclusion: Awareness of nodular fasciitis is crucial to prevent misdiagnosis and unnecessary treatment. Despite its rapid growth, nodular fasciitis generally has an excellent prognosis without long-term consequences., Competing Interests: Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSCC/C419)., (Copyright © 2024 by The Journal of Bone and Joint Surgery, Incorporated.)

Nodular fasciitis (NF) is a benign and self-limiting fibroblastic proliferation that originates from the superficial fascia and extends into the subcutaneous tissue or muscle. It typically manifests in individuals aged 20 to 35 years, with rare occurrences observed in patients over the age of 60 years. We herein report a case involving a 75-year-old man with NF in the right vocal cord. The patient sought medical attention at the Department of Otolaryngology of our hospital because of a 1-month history of hoarseness and breathlessness. The diagnosis was unable to be confirmed through preoperative pathological examination. After admission to our hospital, various examinations were completed and surgical treatment was performed, and the postoperative histopathological findings revealed the presence of NF in the right vocal cord. NF of the vocal cord is a rare clinical entity. Given its rapid progression and propensity for marked infiltration, it often poses diagnostic challenges because it can mimic various malignant soft tissue tumors. Therefore, thorough exclusion of other neoplastic lesions is imperative prior to confirming the diagnosis of NF through pathological examination. Local surgical resection remains the primary treatment modality., Competing Interests: Declaration of conflicting interestsThe authors declare that there are no conflicts of interest.

Aims: Low-grade myofibroblastic sarcoma (LGMS) is a rarely metastasizing myofibroblastic tumour mostly affecting extremities and the head and neck of adults. Histologically, it shows long infiltrative fascicles of spindle cells with moderate nuclear atypia. By immunohistochemistry, it stains positive for smooth muscle actin (SMA) and sometimes for desmin. To date, no recurrent genetic abnormalities have been described. Ubiquitin-specific peptidase 6 (USP6) gene rearrangement is typically found in some benign bone and soft-tissue tumours including nodular fasciitis (NF), among others. Nevertheless, rare cases of USP6-rearranged tumours resembling NF with atypical features have been reported., Methods and Results: One index case of LGMS of the deltoid in a 56-year-old man presented the THBS2::USP6 translocation by RNA sequencing (Archer FusionPlex Sarcoma v2 panel). Further screening of 11 cases of LGMS using fluorescent in situ hybridization (FISH) analysis with a USP6 break-apart probe identified two additional cases. These cases were investigated with RNA-sequencing, and a RRBP1::USP6 translocation was detected in one. The other case was not assessable because of low-quality RNA. Noteworthy, rearranged LGMSs presented distinctive features including variable multinodular/plexiform architecture, prominent vasculature with occasional wall thickening, scattered osteoclast-like multinucleated giant cells, and peripheral lymphoid aggregates., Conclusion: Our findings support the notion that among soft-tissue neoplasms with fibroblastic/myofibroblastic phenotype, USP6 rearrangement is not limited to benign tumours, and warrants further investigation of genetic changes in myofibroblastic sarcomas., (© 2024 John Wiley & Sons Ltd.)

Abstract: We report a case of ischemic fasciitis in a 34-year-old male patient who presented with hard swelling on the anterior aspect of the scalp measuring 5 × 4 cm. He gave a history of wearing a tight turban constantly for many years. The lesion initially presented as redness of the skin, which gradually became a nodular swelling over 2 years. A computed tomography (CT) scan showed conical solid soft tissue attenuation mass. The operative findings were suspicious of neoplasm. However, the microscopic findings were typical of ischemic fasciitis, that is, a zonal pattern with central hypocellular fibrinoid necrosis surrounded by more cellular areas containing prominent proliferating neovessels and fibroblasts resembling granulation tissue. Ischemic fasciitis of the scalp is extremely rare, the present case occurred as a result of ischemia continuously exerted due to wearing a tight turban. This case highlights the importance of eliciting relevant case history and avoids histological misinterpretation of this pseudo-neoplastic lesion., (Copyright © 2023 Copyright: © 2023 Indian Journal of Pathology and Microbiology.)

Ischemic fasciitis is a pseudosarcomatous fibroblastic/myofibroblastic proliferation that shares several overlapping morphological features with proliferative fasciitis and proliferative myositis. Prompted by a recent study that demonstrated FOS gene rearrangements in proliferative fasciitis and proliferative myositis, suggesting that these lesions likely represent examples of "transient neoplasia," we examined a cohort of ischemic fasciitis for similar events. Nine cases of ischemic fasciitis were retrieved from our institutional archives for diagnosis verification, immunostaining for FOSB, and fluorescence in situ hybridization using validated FOS and FOSB break-apart probes. Additionally, RNAseq was performed on a subset of cases. In our cohort, eight out of nine cases of ischemic fasciitis were positive for FOSB IHC, but FISH studies were consistently negative for FOSB and FOS gene rearrangements in all cases. Additionally, RNA sequencing did not detect any gene fusions. These findings suggest that the pathogenesis of ischemic fasciitis is distinct from that of proliferative fasciitis and proliferative myositis., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Aims: This retrospective non-randomised study aims to identify new and rare fusion partners with USP6 in the setting of nodular fasciitis. It has been proven, that nodular fasciitis can harbour different variants of USP6 fusions, which can be used in routine diagnostics and even determine the biological behaviour of the process., Methods: A total of 19 cases of nodular fasciitis examined between 2011 and 2022 at Motol University Hospital in Prague were included into this study. Next to the histopathological evaluation, all cases were assessed using immunohistochemistry, RT-PCR and Anchored multiplex RNA methods. Patient's main demographic characteristics and corresponding clinical data were also analysed., Results: This study presents one novel ( KIF1A ) and five rare examples ( TMP4, SPARC, EIF5A, MIR22HG, COL1A2 ) of fusion partners with USP6 among 19 cases of nodular fasciitis., Conclusion: Identification of USP6 fusion partners in nodular fasciitis helps to understand the biology of such lesions. Moreover, it can be useful in routine histopathological practice of soft-tissues diagnostics, especially in preventing possible misdiagnosis of malignancy., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Fasciitis ossificans is a rare subtype of nodular fasciitis, a benign soft tissue tumor with reactive characteristics. Due to its rapid growth, it is often misdiagnosed as a malignant tumor. While fasciitis ossificans commonly originates from the subcutaneous tissue and can appear throughout the body, it may also arise from extraordinary sites., Case Presentation: We report the first-ever documented case of fasciitis ossificans arising from the penis in a male patient who presented with a tumor on the glans penis. The tumor was surgically resected due to suspicion of penile cancer. Initial histopathological analysis led to a misdiagnosis of squamous cell carcinoma. However, pathological consultation ultimately confirmed the diagnosis of fasciitis ossificans of the penis originating from the glans penis by demonstrating ossification., Conclusion: This case underscores the importance of considering fasciitis ossificans in the differential diagnosis of soft tissue tumors, even in unusual locations such as penile soft tissue., (© 2024. The Author(s).)

Eosinophilic fasciitis (EF) remains a diagnostic challenge due to its rarity and resemblance to scleroderma. This case report aims to provide a cohesive exploration of EF's clinical nuances, emphasizing the importance of accurate diagnosis and effective management. A 52-year-old male developed bilateral forearm and calf hardening, along with erythema, pruritus, and pain four months prior to the presentation in our Clinic. The symptoms initially debuted bilaterally in the forearms and progressed to involve the calves, distal arms, and thighs. Clinical examination revealed symmetrical plaques on forearms and calves, featuring erythematous, hyper, and hypopigmented elements extending proximally, a positive "groove sign" and a moderate difficulty in knee joint flexion. Despite these findings, the patient was generally in good condition, without any other notable clinical signs. Initial laboratory findings showed slightly increased percentual eosinophil levels, elevated C-reactive protein (CRP), normal erythrocyte sedimentation rate (ESR), and negative antinuclear and scleroderma specific antibodies. Magnetic resonance imaging (MRI) demonstrated enhanced fascial signal and thickening while the fascia-muscle biopsy revealed marked edema and inflammatory lymphoplasmacytic infiltrate, consistent with the diagnosis of EF. The patient showed a favorable response to systemic corticosteroids. EF predominantly affects males aged 30 to 60 and is characterized by a sudden onset and unclear etiological factors. Differential diagnosis requires careful exclusion of scleroderma and other mimicking conditions. Diagnostic modalities such as skin-muscle biopsy and MRI reveal characteristic findings like inflammatory infiltrate and fascial thickening. Accurate diagnosis and differentiation from scleroderma are crucial, with early intervention involving glucocorticoids and immunosuppressive agents improving long-term outcomes.

The article describes a clinical case of a benign tumor from smooth muscle cells - piloleiomyoma. The incidence of leiomyoma in the skin is 3-5% of all leiomyomas. A 27-year-old patient applied to a medical institution with complaints about an intradermal formation in the ear region that occurred repeatedly within 5 months after surgical treatment. After the first surgical intervention, the patient was consulted in various medical organizations, where the following diagnoses were made: «nodular fasciitis», «smooth muscle tumor without signs of malignancy» and «non-epithelial spindle cell neoplasm». According to ultrasound examination, the formation with dimensions of 11×9×5 mm reached the mastoid process of the temporal bone and was characterized by increased internal blood flow. After surgical removal of the neoplasm, taking into account the difficulties of differential diagnosis, an immunohistochemical study was conducted. An accumulation of smooth muscle cells was detected in the surface layers of the dermis under the epidermis by the immunohistochemical study with the use of the marker SMA. A study on CD34 protein revealed a high density of blood capillaries and the absence of its expression in smooth muscle cells. The proliferative index (Ki-67) and mitotic activity (PHH-3) of cells was also studied. The index of proliferative activity was less than 2%, mitoses were isolated. Thus, the results of immunohistochemical study proved the conclusion of piloleiomyoma.

Aim: To describe the imaging features of fasciitis ossificans and its histopathological features., Materials and Methods: Using a word search of existing pathology reports at the Mayo Clinic, six cases of fasciitis ossificans were identified. The clinical history, histology, and available imaging of the affected area were reviewed., Results: Imaging consisted of radiographs, mammograms, ultrasound images, bone scintigraphs, computed tomography (CT), and magnetic resonance imaging (MRI) images. All cases demonstrated a soft-tissue mass. The characteristic MRI appearance was a T2 hyperintense enhancing mass with surrounding soft-tissue oedema. Peripheral calcifications were seen on radiographs, CT, and/or ultrasound. Histological sections showed distinct zonation, with nodular fasciitis-like zones of myofibroblastic proliferation, which merged with osteoblasts that rim the ill-defined trabeculae of woven bone and became continuous with the mature lamellar bone surrounded by a thin layer of compressed fibrous tissue., Conclusion: Imaging features of fasciitis ossificans are that of an enhancing soft-tissue mass located within a fascial plane with prominent surrounding oedema and mature peripheral calcification. Imaging and histology are that of myositis ossificans but occurring within the fascia. It is important that radiologists are aware of the diagnosis of fasciitis ossificans and appreciate its similarity to myositis ossificans. This is particularly important in anatomical locations with fascias but no muscle. Given the radiographic and histological overlap between these entities, nomenclature that encompasses both could be considered in the future., (Copyright © 2023. Published by Elsevier Ltd.)

Ubiquitin-specific protease 6 ( USP6 ) rearrangements have been identified in aneurysmal bone cyst, nodular fasciitis, myositis ossificans, fibro-osseous pseudotumour of digits and cellular fibroma of tendon sheath. These entities show clinical as well as histological overlap, suggesting they are all clonal neoplastic belonging to the same biological spectrum and referred to as ' USP6 -associated neoplasms'. They all show a characteristic gene fusion formed by juxtaposition of the USP6 coding sequences to the promoter regions of several partner genes, leading to USP6 transcriptional upregulation., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2023. No commercial re-use. See rights and permissions. Published by BMJ.)

Nodular fasciitis (NF) has a low incidence, many classification subtypes and large histological variations. We describe a 17-month-old child who presented with a mass in the right cavity of auricular concha that was successfully cured by 2 procedures. In pediatric patients with fibroproliferative lesions, the possibility of NF should be excluded to avoid misdiagnosis and overtreatment.

Nodular fasciitis is a rare, benign lesion characterized by the pseudosarcomatous proliferation of fibroblasts and myofibroblasts. Accurate diagnosis presents a unique challenge for otolaryngologists, as nodular fasciitis frequently mimics malignancy clinically; however, it can be distinguished from malignancy by subtle findings on pathology. A diagnosis of nodular fasciitis should be considered for any irregular or rapidly growing lesion of the head and neck area, as accurate diagnosis is particularly important to avoid overtreatment in cosmetically sensitive regions.

Since the discovery of USP6 gene rearrangements in aneurysmal bone cysts nearly 20 years ago, we have come to recognize that there is a family of USP6-driven mesenchymal neoplasms with overlapping clinical, morphologic, and imaging features. This family of neoplasms now includes myositis ossificans, aneurysmal bone cyst, nodular fasciitis, fibroma of tendon sheath, fibro-osseous pseudotumor of digits, and their associated variants. While generally benign and in many cases self-limiting, these lesions may undergo rapid growth, and be confused with malignant bone and soft tissue lesions, both clinically and on imaging. The purpose of this article is to review the imaging characteristics of the spectrum of USP6-driven neoplasms, highlight key features that allow distinction from malignant bone or soft tissue lesions, and discuss the role of imaging and molecular analysis in diagnosis., (© 2022. The Author(s), under exclusive licence to International Skeletal Society (ISS).)

Primary aneurysmal bone cyst, nodular fasciitis, myositis ossificans and related lesions as well as fibroma of tendon sheath are benign tumors that share common histological features and a chromosomal rearrangement involving the ubiquitin-specific peptidase 6 (USP6) gene. The tumorigenesis of this tumor spectrum has become complex with the identification of an increasing number of new partners involved in USP6 rearrangements. Because traumatic involvement has long been mentioned in the histogenesis of most lesions in the USP6 spectrum and they morphologically resemble granulation tissue or callus, we attempted to shed light on the function and role USP6 partners play in tissue remodelling and the repair process and, to a lesser extent, bone metabolism., (©The Author(s) 2023. Open Access. This article is licensed under a Creative Commons CC-BY International License.)

Proliferative fasciitis (PF) is a benign fibroblastic reaction with histological and clinical characteristics that overlap with those of malignant soft tissue tumors; thus, it is referred to as a pseudosarcomatous reaction. It continues to be an important cause of diagnostic error and overtreatment. The childhood PF subtype has some distinct histological and immunohistochemical characteristics that make differential diagnosis with malignant tumors even harder, especially with sarcoma. These proliferations generally occur in the lower limbs, and the periorbital region is a rare location of appearance. Here, we describe a case of childhood subtype PF in a 16-year-old girl located in the periorbital area. To the best of our knowledge, this is the first reported case of childhood subtype PF in the periorbital area, and the third case if PF subtypes are not taken into account.

Eosinophilic fasciitis (EF), defined as diffuse fasciitis with eosinophilia by Shulman in 1974, is a disease with unknown etiology and whose pathogenesis is still being researched. The diagnosis is based on the clinical aspects (skin induration with an "orange peel" appearance), the lab results (eosinophilia, increased inflammatory markers), the skin biopsy with the pathognomonic histopathological result, as well as the typical MRI changes. The treatment includes glucocorticoids and immunosuppressive drugs. Due to severe refractory cases, the treatment remains a challenge. EF is still a disease with potential for further research.

Myxofibrosarcoma (MFS) is a fibroblastic/myofibroblastic neoplasm with a variably myxoid stroma. Histologically, MFS shows a wide spectrum of cellularity, pleomorphism and proliferative activity. Because of its variable morphology and lack of discriminatory markers, MFS can be difficult to distinguish from some benign soft-tissue tumors, especially nodular fasciitis (NF). Glucose transporter 1 (GLUT-1) is expressed in a variety of malignant mesenchymal tumors. In the current study, we evaluated GLUT-1 expression to determine its value in distinguishing MFS from NF. Tissue specimens from 14 MFS cases and 16 NF cases were sectioned and stained for GLUT-1 using immunohistochemistry. The percentage of GLUT-1-positive cells was scored as follows: 0 (no staining), 1+ (1-19%), 2+ (20-50%) and 3+ (>50%). Samples with a score of 1+ were defined as GLUT1-expressing samples. GLUT-1 expression was seen in all 14 MFS cases, whereas only 6 NF cases (37.5%) were positive for GLUT-1 and were scored 1+. Notably, 2-3+ GLUT-1 expression was found in 86% of MFS cases and 0% of NF cases. Our results indicate that GLUT-1 is a highly sensitive immunohistochemical marker for MFS and may be useful for the differential diagnosis of MFS and NF., (©The Author(s) 2023. Open Access. This article is licensed under a Creative Commons CC-BY International License.)

Eosinophilic dermatoses are a heterogeneous group of rare diseases that histopathologically display the defining pattern of an eosinophil-rich dermal infiltrate. In these eosinophilic dermatoses, a histopathologic pattern called flame figures, which result from degranulation of eosinophils in the tissue, can be observed. Although eosinophil granulocytes can also be detected in other dermatoses such as atopic dermatitis, urticaria, prurigo and bullous pemphigoid, the eosinophil-rich infiltrate is decisive for classic eosinophilic dermatoses. Accordingly, eosinophilic dermatoses include hypereosinophilic syndrome, eosinophilic fasciitis, granuloma faciale, pustular sterile eosinophilia, and angiolymphoid hyperplasia with eosinophilia. These eosinophilic dermatoses display clinical different patterns and are discussed in this article, as well as the interesting eosinophils and novel therapeutic options., (© 2022. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Nodular fasciitis (NF) is a myofibroblastic proliferation that is uncommonly present in pediatric patients. These benign neoplasms can masquerade as more insidious sarcomatous proliferations on both clinical exam and initial histopathologic review, often prompting undue concern in patients, parents, and providers. While immunohistochemical analysis of NF can be variable, adding to the diagnostic uncertainty, molecular analysis documenting ubiquitin-specific protease 6 (USP6) gene rearrangement can help confirm the diagnosis as an association between NF and USP6 overexpression was first identified 10 years ago in an analysis that found rearrangements of the involved locus in over 90% of studied samples. In this report, we review one case of NF located on the chin of a nine-year-old girl in which molecular testing was essential to secure the correct diagnosis, and provide a summary of documented cases of USP6 overexpression in transient pediatric neoplasms., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Objective: To study the clinicopathological, immunophenotypic and molecular genetic characteristics of nodular fasciitis (NF) in unusual sites. Methods: A total of 50 cases of NF diagnosed between January 2015 and January 2021 were reviewed in the Department of Pathology, Henan Provincial People's Hospital, and the clinical and pathologic data were analyzed. Among them, 14 cases from unusual sites were included in this study. Immunohistochemical (IHC) staining was used to detect the expression of related proteins, and fluorescence in situ hybridization (FISH) was used to detect the breakage of the USP6 gene. Results: There were seven males and seven females in the 14 NF respectively. The lesions were located in the extremities, perineum, breast, wrist joints, the gap between lumbar vertebra 4/5, and in eight cases there was involvement of unusual tissues (six cases in skeletal muscle, one case in nerve root, and one case was intravascular). The tumor boundary was unclear with infiltrating growth. Spindle-shaped myofibroblasts were arranged in bundles or chaotically, with mild pleomorphic, small nucleoli and various mitotic figures. The tumor stroma showed collagenization to myxoid degeneration with erythrocyte extravasation and infiltration of inflammatory cells. IHC staining showed that the spindle cells expressed SMA focally or partially, and p16 diffusely and strongly. FISH showed that 12 of 14 cases had USP6 gene breakage, and two of them occurred in the intrathoracic skeletal muscle with the red signal amplification of USP6 gene. Conclusions: NF in unusual sites shows similar clinicopathological and genetic characteristics to classic NF, but the tumor mostly has infiltrating borders, non-specific and strong expression of p16, and USP6 red signal amplification. The pathological diagnosis of NF in rare sites should be highly vigilant.

Background: Cranial fasciitis (CF) is a benign (myo)fibroblastic proliferation of children. Typical presentation consists of a rapidly growing solitary mass on the temporal or parietal cranium in the first 2 years of age. CF is characterized by a rapid growth followed by a relative slowdown and even growth arrest. The finding of somatic USP6 gene rearrangements demonstrating clonality in CF together with its clinical behavior places it in the category of diseases recently termed "transient neoplasia." Methods: Histological, immunohistochemical, and molecular findings of 18 patients with CF were retrospectively studied. Results: The tumor typically presented as a painless rapidly enlarging mass in the temporal region. Sixty-six percent of the cases harbored USP6 gene rearrangement. Nine patients were treated with gross total resection (GTR) and 9 with subtotal tumor resection (STR). Two patients treated with GTR had recurrence. Five patients treated with STR had progression-free disease for at least 10 months after surgery and in four patients the tumor regressed spontaneously a median 16 months after surgery. Conclusions: In this largest series to date, we reported the clinicopathological, immunohistochemical, and molecular findings of 18 pediatric cases of CF with emphasis on the clinical growth pattern of these tumors.

A 4-year-old patient with a left orbital mass was admitted to the Department of Ophthalmology of the First Affiliated Hospital of Zhengzhou University. After clinical and imaging examinations, the left orbital mass lesion was removed under general anesthesia. Postoperative pathological examination confirmed orbital cranial fasciitis. The appearance and imaging result of the patient were normal at postoperative 7 months.

Background: Nodular Fasciitis is a benign fibroblastic proliferation in soft tissues, which mostly occurs in the upper extremities, trunk, head and neck region. It is rarely reported to occur in the breast., Case Presentation: Herein, we present sonograms of nodular fasciitis in the breast at different durations in three cases. In Case 1, we provided the longest follow-up time in all literatures. In Case 2 and Case 3, we provided the automated breast ultrasound finding of breast nodular fasciitis for the first time., Conclusion: Nodular Fasciitis shows clinical features and ultrasonography findings are similar to those of breast cancer. For superficially located breast lesions with a single and rapid growth, nodular fasciitis may be considered in the differential diagnosis of benign entities resembling malignant tumors on breast imaging., (© 2022. The Author(s).)

We report a case of eosinophilic fasciitis triggered by strenuous physical activity, which did not relapse during the follow-up period. We ascertained that interleukin-33 (IL-33) was released from the vascular endothelial cells after intense exercise, inducing type 2 innate lymphocytes (ILC2) and causing fasciitis. A healthy woman experienced itching on both limbs a few hours after a game of drumming. Her hand, knee joints, and legs gradually swelled up with groove signs along the superficial veins. White blood cell and eosinophil counts were significantly elevated. Magnetic resonance imaging revealed a high signal at the fascia on both lower limbs. Histopathological findings of the left lower limb tissue specimen showed edematous fascia with eosinophils. No relapse of eosinophilic fasciitis was observed after finishing treatment with prednisolone. Immunological staining for IL-4, IL-5, IL-33, tumor necrosis factor-α, and interferon-γ was performed on the fascial tissue. Both IL-4 and IL-5 were stained on the lymphocytes at the muscle and fascia levels; however, CD3 and CD4 were unstained in these cells, suggesting that those cells were ILC2. Tumor necrosis factor-α and interferon-γ were unstained. Vascular endothelial cells in the fascia strongly expressed IL-33. Eosinophilic fasciitis may be associated with type 2 immunity triggered by IL-33 in the current case., (© 2022 Asia Pacific League of Associations for Rheumatology and John Wiley & Sons Australia, Ltd.)

Cellular fibroma of tendon sheath (CFTS) is a rare, benign myofibroblastic neoplasm of tenosynovial soft tissues closely resembling nodular fasciitis (NF), but is histomorphologically distinct from classic fibroma of tendon sheath (FTS). We report a case of a pediatric patient with thumb swelling clinically concerning for arthritis with a biopsy demonstrating myofibroblastic proliferation with features consistent with NF/CFTS, and molecular studies confirming the presence of a USP6 gene fusion (TNC-USP6). This case highlights a unique clinical presentation of CFTS in a pediatric patient mimicking an inflammatory or reactive/non-neoplastic musculoskeletal disorder and the increasingly crucial role of molecular testing to differentiate a reactive myofibroblastic process from a neoplasm. Moreover, this report identifies TNC as a new fusion partner to USP6 fusion partner adding to our growing understanding of the USP6-rearranged family of tumors.

Periosteal fasciitis (PF), a subtype of nodular fasciitis, is an uncommon benign soft-tissue mass that originates from the periosteum or tissues adjacent to bones. PF has rarely seen in children, especially involving in the mandible. This case report presents a rare case of PF originating from the periosteum of the mandible in an 11-year-old girl. She was referred to our hospital with fast-growing painless swelling in her left mandible. Computed tomography revealed an exophytic juxtacortical mass eroding the lower part of the left mandible and lower mandibular cortex with a periosteal reaction. The mass showed low signal intensity on T1-weighted magnetic resonance imaging (MRI) and high signal intensity on T2-weighted MRI. The apparent diffusion coefficient (ADC) of the lesion found to be moderate. Dynamic contrast-enhanced MRI revealed a gradual increment pattern in the central region of the mass. On 18F-fluorodeoxyglucose (FDG) positron-emission tomography/computed tomography (PET/CT), relatively high 18F-FDG uptake was observed on the early scan and the 18F-FDG uptake was declined on the delayed scan. The clinical and conventional radiological findings of the mass were suggestive of malignancy. However, the findings of ADC and dynamic MRI and dual-time-point FDG-PET/CT favored benign etiology over malignant etiology. Histological and immunohistochemical findings along with reactive ossification of the periosteum confirmed the diagnosis of PF. Currently, comprehensive examinations, such as clinical, imaging, and histopathological examinations, are recommended for the definitive diagnosis of PF, while MRI and dual-time-point FDG-PET/CT could have a potential usefulness to differentiate from malignancy., (© 2021. The Author(s).)

The self-limited nature of nodular fasciitis (NF) is well-known but its precise mechanism has not yet been clarified. We observed that "young" NF (preoperative duration <1 month) consistently contains a higher percentage (~80%) of USP6 break-apart FISH signals than "old" NF (preoperative duration >3 months) (~20%). Thus, we hypothesized that our original observation may reflect a connection with the self-limited nature of NF. Seventeen cases with reliable data concerning the onset were selected, thus approximating the lifetime of each tumor. Besides the USP6 interphase FISH examination, we also checked the most common MYH9-USP6 fusion using RT-PCR. Because of the known pathways of the tumorigenesis of NF, the mRNA level of USP6, TRAIL, IFN-beta, JAK1, STAT1, STAT3, JUN, and CDKN2A was measured using qRT-PCR. Regarding proteins, USP6, p16, p27, TRAIL, and IFN-beta were examined using immunohistochemistry. Targeted gene panel next-generation sequencing (NGS) of three cases was additionally performed. We found a strong negative correlation (p = 0.000) between the lifetime and percentage of USP6 break-apart signals and a strong positive relationship (p = 0.000) between USP6 break-apart signals and mitotic counts. Results of immunostainings, along with qRT-PCR results, favored the previously-suggested USP6-induced negative feedback mechanism through activation of TRAIL and IFN-beta, likely resulting in apoptosis and senescence of tumor cells harboring USP6 fusions. Targeted-NGS resulted in the detection of several variants, but no additional recurrent changes in the pathogenesis of these tumors. We revealed on a cellular level the USP6-induced negative feedback mechanism. In conclusion, we emphasize that in "old" NF, the percentage of USP6 break-apart FISH signals can be as low as 14-27% which can be very important from a differential diagnostic point of view. We emphasize that a careful examination and interpretation of the NGS data is needed before clinical decision-making on treatment., (© 2021. The Author(s).)

Nodular fasciitis (NF) is a benign, self-limiting, reactive soft tissue tumor that is composed of fibroblasts and myofibroblasts and is often misdiagnosed as a malignant lesion. Nodular fasciitis is often reported in adults but rarely seen in children. We report the case of a 3-year-old girl with a rapidly growing NF in the left nasal cavity. The initial biopsy suggested the possibility of a spindle cell tumor or low-grade malignant tumor, respectively. The child underwent complete excision of the tumor. With the help of immunohistochemistry and pathological consultation, the final diagnosis was confirmed as NF. There was no recurrence during an 18-month follow-up period.

Nodular fasciitis is a benign, self-limited, pseudosarcomatous neoplasm that is cytogenetically characterized by recurrent USP6 gene rearrangement. Involvement of the breast by nodular fasciitis is very rare with only a few documented cases. It can clinically, radiologically and histologically mimic a malignancy, posing significant diagnostic challenges to clinicians, radiologists, and pathologists. In this study, we report 2 cases of nodular fasciitis occurring in the female breast, reviewing the literature and emphasizing the application of fluorescence in situ hybridization analysis of USP6 gene rearrangement in its diagnosis and differential diagnosis., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Inflammation early in life can prime the local immune milieu of peripheral tissues, which can cause lasting changes in immunological tone that confer disease protection or susceptibility 1 . The cellular and molecular mechanisms that prompt changes in immune tone in many nonlymphoid tissues remain largely unknown. Here we find that time-limited neonatal inflammation induced by a transient reduction in neonatal regulatory T cells causes a dysregulation of subcutaneous tissue in mouse skin. This is accompanied by the selective accumulation of type 2 helper T (T H 2) cells within a distinct microanatomical niche. T H 2 cells are maintained into adulthood through interactions with a fibroblast population in skin fascia that we refer to as T H 2-interacting fascial fibroblasts (TIFFs), which expand in response to T H 2 cytokines to form subcutaneous fibrous bands. Activation of the T H 2-TIFF niche due to neonatal inflammation primes the skin for altered reparative responses to wounding. Furthermore, we identify fibroblasts in healthy human skin that express the TIFF transcriptional signature and detect these cells at high levels in eosinophilic fasciitis, an orphan disease characterized by inflammation and fibrosis of the skin fascia. Taken together, these data define a previously unidentified T H 2 cell niche in skin and functionally characterize a disease-associated fibroblast population. The results also suggest a mechanism of immunological priming whereby inflammation early in life creates networks between adaptive immune cells and stromal cells to establish an immunological set-point in tissues that is maintained throughout life., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Aneurysmal (ABC) and simple bone cysts (SBC) have been traditionally distinguished by radiological and histopathological features. However, there is some radiological and histopathological overlap between ABC and SBC. ABC is characterised by USP6 fusions while, recently, NFATC2 fusions have been found in a large proportion of SBC. Identifying these fusions may assist in confirming the diagnosis of either ABC or SBC. To elaborate the potential benefit of molecular testing, we report a prospective series of 19 consecutive bone cysts with comprehensive radiological, histopathological and molecular diagnostics. Integrating radiological, histopathological and molecular findings, 11 cysts were diagnosed as SBC and 8 as ABC. Radiologically, 6 of 11 SBC and 6 of 8 ABC were diagnosed as ABC. Fibrin-like collagen deposits were identified in 8 of 11 (73%) SBC and 3 of 8 (38%) ABC. Nodular fasciitis-like areas were identified in 6 of 8 (75%) ABC and in 7 of 11 (64%) SBC. A USP6 fusion was identified in all 8 ABC, including a novel RBM5-USP6 fusion. An NFATC2 fusion was found in 7 of 11 SBC (FUS-NFATC2 fusion in 5 and EWSR1-NFATC2 in 2 cases). There is radiological and histopathological overlap between SBC and ABC in a significant proportion of cases. A diagnosis of ABC is frequently suggested radiologically in SBC, and fibrin-like deposits, thought to be specific for SBC, may be found in some ABC. Molecular testing may significantly improve diagnostic accuracy in bone cysts., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nodular fasciitis is a benign, self-limited, pseudosarcomatous neoplasm that can mimic malignancy due to its rapid growth, cellularity, and mitotic activity. Involvement of the breast is rare and diagnosis on biopsy can be challenging. In this largest series to date, we examined the clinicopathologic and molecular characteristics of 12 cases of nodular fasciitis involving the breast/axilla. All patients were female, with a median age of 32 years (range 15-61). The lesions were 0.4 to 5.8 cm in size (median 0.8). All cases presented as palpable masses, and two patients had overlying skin retraction. Microscopically, lesions were relatively well-circumscribed nodular masses of bland myofibroblastic spindle cells within a variably myxoid stroma. Infiltrative growth into adipose tissue or breast epithelium was frequent. Mitotic figures were present in all cases, ranging from 1 to 12 per 10 high-power fields (median 3). Immunohistochemically, all cases expressed smooth muscle actin and were negative for pan-cytokeratin, p63, desmin, CD34, and nuclear beta-catenin. Targeted RNA sequencing performed on 11 cases identified USP6 gene fusions in eight; one additional case was positive by break-apart fluorescence in situ hybridization. The common MYH9-USP6 rearrangement was detected in four cases; another case had a rare alternative fusion with CTNNB1. Three cases harbored novel USP6 gene fusions involving NACA, SLFN11, or LDHA. All fusions juxtaposed the promoter region of the 5' partner gene with the full-length coding sequence of USP6. Outcome data were available for eight patients; none developed recurrence or metastasis. Five patients elected for observation without immediate excision, and self-resolution of the lesions was reported in three cases. Albeit uncommon, nodular fasciitis should be considered in the differential diagnosis of breast spindle cell lesions. A broad immunohistochemical panel to exclude histologic mimics, including metaplastic carcinoma, is important. Confirmatory detection of USP6 rearrangements can aid in classification, with potential therapeutic implications., (© 2021. The Author(s), under exclusive licence to United States & Canadian Academy of Pathology.)

Nodular fasciitis is usually a benign lesion genetically characterized by ubiquitin-specific protease 6 ( USP6 ) rearrangements. We present a case of a 10-year-old boy with a 1.5-week history of a painless mass on the right chest wall, which was excised. A histomorphologically malignant tumor with pronounced pleomorphism, atypical mitotic figures, and a myoid immunophenotype was observed. The methylation profile was consistent with nodular fasciitis and fluorescence in situ hybridization confirmed USP6 rearrangement. Using Archer Fusion Plex (Sarcoma Panel) and RNA sequencing, a collagen, type VI, alpha 2 ( COL6A2 ) -USP6 gene fusion was subsequently identified. Furthermore, DNA clustering analysis also showed a match with nodular fasciitis. During the follow-up of 22 months, no recurrence or metastasis occurred. In conclusion, we describe a clinically benign, histomorphologically malignant mesenchymal neoplasm with a myoid immunophenotype, and a genetic and epigenetic profile consistent with nodular fasciitis. In such cases, molecular analysis is a useful adjunct to avoid unnecessary overtreatment.