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PRRX1-fused mesenchymal neoplasm is a recently identified, rare subcutaneous soft tissue neoplasm that is characterized by fusion of PRRX1 (exon 1) with NCOA1 (exon 13) in the majority of reported cases. Although initially considered to be fibroblastic, a possibility of neural or neuroectodermal differentiation has been suggested in a subset of cases. We report a 26-year-old female with a 4.0 cm painless mass located in the subcutis of the left thigh. Microscopically, the tumor was well-circumscribed and multinodular and was composed of relatively monomorphic ovoid to spindle cells arranged in loose fascicles, trabeculae, and cords within alternating myxoid and fibrous matrix, and vascularized stroma. Mitotic figures were scarce and necrosis was not observed. By immunohistochemistry, the neoplastic cells demonstrated focal co-expression of S100 protein and SOX10 and were negative for epithelial membrane antigen, smooth muscle actin, desmin, CD34, STAT6, HMB45, Melan-A, and MUC4. The expression of Rb1 was retained. Targeted RNA-sequencing identified a novel transcript fusion of PRRX1 (exon 1)::NCOA1 (exon 15), which was further confirmed by reverse transcription polymerase chain reaction and Sanger sequencing. The tumor was narrowly excised and no tumor recurrence or metastasis was identified after 13 months of follow-up. In summary, we report a new case of PRRX1-fused mesenchymal neoplasm, expanding the molecular genetic spectrum and providing further support for possible neural or neuroectodermal differentiation of this emerging soft tissue tumor entity., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Pagetoid Spitz nevus is a rare subtype of Spitz nevus usually found on the lower extremities, particularly on the thigh of women. As a rare and under-recognized entity that can be misdiagnosed as melanoma, further characterization of clinical and histopathological features is needed to improve its recognition., Methods: A retrospective analysis of all melanocytic neoplasms from the thigh diagnosed over a 3-year period., Results: Fifty-five (15.4%) of the 357 melanocytic neoplasms on the thigh were Spitz nevi, the majority of them occurring in women (87.3%). Of the 55 Spitz nevi, 33 (60.0%) were pagetoid Spitz nevi, 14 (25.5%) were Reed nevi, and eight (14.5%) were conventional Spitz nevi. The mean age of patients with pagetoid Spitz nevi was 47.2, the majority being women (84.9%). Pagetoid Spitz nevi were small, with a mean histopathologic diameter of 4 mm, and often junctional (63.6%). Compared to Clark nevi of the thigh, pagetoid Spitz nevi comprised significantly more solitary melanocytes with a greater degree of scatter., Conclusions: These results suggest that Spitz nevi and, in particular, pagetoid Spitz nevi constitute a significant percentage of nevi on the thigh. Previously reported benign clinical and histopathological features of pagetoid Spitz nevi are confirmed in this study., (© 2020 John Wiley & Sons A/S . Published by John Wiley & Sons Ltd.)

Background: Myxoid liposarcoma typically presents as a deep-seated mass in the lower extremity of adults. Presentation as a primary subcutaneous tumor is rare. Here we discuss clinicopathologic characteristics of three such cases and their differential diagnosis to alert dermatopathologists to this unusual clinical presentation of a potentially aggressive entity., Methods: Cases of myxoid liposarcoma were retrieved from archives and consultation files. Inclusion required location above the subcutaneous fascia with no evidence of a metastatic origin. Clinicopathologic features were retrospectively reviewed. Fluorescence in situ hybridization for DDIT3 (CHOP) gene rearrangement was performed on all cases., Results: The tumors affected young adults (two males and one female, mean 36 years, range 32-40 years). No prior history of myxoid liposarcoma or deep soft tissue mass was identified. The tumors occurred in the foot, thigh and hand. All demonstrated multilobular architecture with abundant myxoid stroma, prominent branching capillary vascular network and lipoblastic differentiation. No dermal involvement was seen. Round cell features were identified in one case and represented <5% of the tumor. All patients remain disease-free following local excision only at 6, 8 and 13 months., Conclusions: Myxoid liposarcoma can rarely present as a primary subcutaneous mass and should be considered in the differential diagnosis of cutaneous myxoid tumors in adults., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

We report the case of a two patients who presented with a solitary, asymptomatic, angiomatoid nodule on the right thigh. Histopathological finding showed a poorly circumscribed lesion, located in the dermis. The morphological aspect strongly suggested the diagnosis of atypical fibrous histiocytoma (AFH), but surprisingly, the neoplastic cells were diffusely CD30+, with a membrane staining devoid of paranuclear dot. The lesions were tested for p80/ALK1 expression. Surprisingly, we found a diffuse cytoplasmic positivity. Interestingly, using break-apart fluorescent in situ hybridization (FISH), we evidenced an ALK rearrangement in nearly 50% of the neoplastic cells. The expression of CD30 and ALK1 with ALK gene rearrangement raised the possibility of three diagnoses: a primary cutaneous anaplastic large cell lymphoma (ALCL), a cutaneous inflammatory myofibroblastic tumor (IMT), an AFH of the skin associated with ALK gene rearrangement and CD30 positivity. The three hypotheses were discussed and finally, although p80/ALK1 expression and cytogenetic abnormalities in fibrous histiocytoma (FH) are not yet reported to the best of our knowledge, we favored the diagnosis of AFH., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Importance: Extramammary Paget disease (EMPD) is an uncommon tumor that presents in apocrine-rich skin as an irregular, pruritic plaque. Histopathologically, EMPD consists of an intraepidermal proliferation of atypical epithelioid cells. Rarely, the tumor cells contain intracytoplasmic melanin pigment, and the lesion clinically and histopathologically can mimic a melanocytic proliferation., Observations: A 51-year-old female with a history of breast carcinoma presented with a pigmented patch on her right thigh of 6 months duration. The clinical impression was an atypical melanocytic nevus. Histopathologic examination revealed an intraepidermal proliferation of epithelioid cells along the dermal-epidermal junction with pagetoid migration. The tumor cells exhibited increased cytoplasm containing conspicuous melanin pigment and enlarged oval-irregular nuclei. Immunohistochemical studies showed the tumor cells to be strongly and diffusely positive for cytokeratin 8/18, cytokeratin 7 and p63; focally and weakly positive for epithelial membrane antigen (EMA), but negative for cytokeratin 5/6, Cam5.2, carcinoembryonic antigen (CEA), human melanoma black 45 (HMB-45), tyrosinase and Sox-10, supporting the diagnosis of pigmented EMPD. The lesion was subsequently excised, and the patient is free of disease after 24 months., Conclusion: We present this unusual case of pigmented EMPD arising on the thigh to draw attention to the entity and to underscore the potentially misleading clinical, histopathologic and immunophenotypic features that mimic other cutaneous intraepidermal lesions., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Benign lymphangioendothelioma represents a rare lymphatic vascular proliferation characterized by proliferation of irregular and thin-walled vessels dissecting amongst dermal collagen. Immunohistochemical analysis has been lacking in most previously reported cases., Methods: Herein, we report the clinical and histopathologic characteristics of four cases of benign lymphangioendothelioma. Immunohistochemical study was completed for all lesions., Results: All lesions presented as large, red to brown patches or plaques. Three lesions were located on the thigh and one lesion was located on the neck. Histopathologically, all lesions showed proliferation of anastomotic or retiform thin-walled vessels with a single layer of endothelial cells that dissect the dermis. D2-40 and Prox1 immunostains were positive and Wilms tumor 1 (WT-1) immunostain was negative in all cases., Conclusion: Benign lymphangioendothelioma represents a lymphatic vascular proliferation. A lack of expression of WT-1 suggests it represents a lymphatic vascular malformation., (© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

A Morel-Lavallée lesion (MLL) is a posttraumatic soft-tissue injury characterized by an accumulation of blood, lymph, and other physiologic breakdown products between subcutaneous tissue and underlying fascia. It was first described as occurring over the proximal lateral thigh, but it has since been documented at various anatomic locations. Diagnosis is typically made by careful physical examination and a radiographic analysis, most commonly with magnetic resonance imaging (MRI). Recently, musculoskeletal ultrasound (US) has been recognized as a useful adjunct to and potential replacement for MRI in the diagnosis and monitoring of an MLL. We present a case report of a patient with an MLL of the knee. We obtained magenetic resonance (MRI) and US images at the time of diagnosis, and follow-up US images during convalescence. By doing so, we were able to identify several key sonographic findings of an MLL at this location and compare them with MRI. Although there have been several published reports to date that describe the use of musculoskeletal US in the diagnosis of MLL, this is the first of which we are aware that does so at the knee., (Copyright © 2013 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.)

Dermal mucinoses are a heterogeneous group of disorders characterized by abnormal deposition of dermal mucin, an amorphous substance composed of hyaluronic acid and sulfated glycosaminoglycans. We describe two cases of dermal mucinosis in the setting of chronic venous insufficiency. Both patients presented with painful, edematous lower extremity plaques. Biopsies of all lesions showed striking dermal mucin deposition, a slight increase in small blood vessel density, slightly thickened vessel walls and no inflammation. Neither patient showed laboratory or clinical findings consistent with a secondary mucinosis such as thyroid dysfunction, lupus erythematosus, dermatomyositis, scleroderma, granuloma annulare, graft-vs.-host disease or mucin deposition post-ultraviolet or photochemotherapy treatment. Both patients were diagnosed with localized cutaneous mucinosis secondary to venous insufficiency. The clinicopathological features of this entity are described, and a pathogenic mechanism is proposed.

A pilomatricoma, or Malherbe's calcifying epithelioma, is an uncommon tumor originating from hair matrix cells. It is clinically characterized by a solitary, firm nodule. As the skin overlying the pilomatricoma may change in color and texture, its clinical presentation can vary. We report an unusual case of pilomatricoma with associated anetoderma on the lower extremity of a 12-year-old girl. Histology revealed a thinned dermis replaced by myxomatous tissue between the surface and a deep-seated tumoral mass. This mass is formed of irregular islands of basaloid cells, shadow cells, calcified areas and discrete inflammatory and foreign-body reactions surrounding it. Anetodermic cutaneous changes may occur in pilomatricomas without histological evidence of triggering factors.

Desmoplastic fibroblastoma is a rare, benign, soft tissue tumor. We describe a case of superficial desmoplastic fibroblastoma presenting as a protruding nodule. A 41-year-old woman presented with a painless, firm, elevated nodule with ulceration on her left thigh. Histological examination from total excision showed a well-circumscribed tumor in the dermis, which comprised of spindle, oval and stellate cells arranged in a haphazard fashion, accompanied by abundant collagenous stroma and inconspicuous vasculature. Immunohistochemically, the tumor cells were positive for vimentin, and focally positive for alpha-smooth muscle actin and muscle-specific actin, but negative for CD34, S-100 protein, desmin and beta-catenin. We diagnosed this case as desmoplastic fibroblastoma arising in the dermis and superficial subcutaneous tissue., (Copyright Blackwell Munksgaard 2008.)

Extraskeletal osteosarcoma is an uncommon neoplasm that usually arises in the deep soft tissues, especially in the lower extremities, with rare cases involving the subcutis or dermis. We report a 60-year-old man with an enlarging cutaneous mass in the right lower thigh. An incisional skin biopsy showed a well-defined, but non-encapsulated neoplasm, characterized by extensive cartilage with marked cellularity, atypia and high mitotic activity, involving the dermis and subcutis. Although osteoid or bone was not observed, a diagnosis of cutaneous chondroblastic osteosarcoma was suggested after excluding an origin in bone or other primary tumor sites by imaging techniques. Histopathologic features of the surgical specimen were characteristic, with a predominant high-grade chondroid component together with focal fibrosarcomatous zones, areas of multinucleated giant cells and foci of bone and osteoid formation. The patient underwent postoperative chemotherapy and is currently alive with pulmonary metastases 15 months after surgery. In summary, we report a unique case of cutaneous osteosarcoma of the chondroblastic subtype, diagnosed on incisional skin biopsy despite the absence of osteoid or bone during tumor sampling. As a rule, when an obviously malignant 'chondrosarcoma' is identified, one should always consider this entity.

Zygomycosis is an aggressive infection by an angioinvasive fungus seen in patients with defects in phagocytosis. We describe a neutropenic child with primary cutaneous Rhizopus infection presenting with a bull's-eye appearance. The patient was treated with aggressive surgical debridement along with amphotericin B followed by skin grafting, with full recovery.

Juvenile xanthogranuloma is the most common non-Langerhans cell histiocytosis of infancy and childhood. It is a benign disorder that usually regresses spontaneously, more often without or with limited skin changes. The clinical features are very pleomorphic and recognition of the atypical presentations should facilitate the diagnosis. We report a 9-month-old boy who had an extensive, atrophic lesion on the proximal thigh that followed the course of the congenital giant form. The large size of the lesion does not alter the clinical course or result in extracutaneous involvement, which remains rare. However, uncommon clinical presentations raise the problem of differential diagnosis, requiring biopsy to eliminate other tumors with a less favorable prognosis.

The in vivo detection of growing collateral vessels following arterial occlusion is difficult in small animals. We have addressed the feasibility of performing high resolution time-of-flight angiograms to monitor the growth of collateral vessels after femoral artery occlusion in mice. We will also present a low-pass quadrature birdcage coil construction with a sufficient signal-to-noise ratio to produce high resolution. After a 4-month recovery period a C57BL/6 mouse with a surgical occlusion of the right femoral artery was used to assess the image quality and time requirements to produce magnetic resonance angiograms sufficient to assess collateral artery development using a two-dimensional gradient echo sequence. At a resolution of 100 x 100 x 100 microm and a matrix size of 256 x 128 x 256 for a 2.56 cm isometric volume, three scans were performed with one, two and four repetitions resulting in signal-to-noise ratios for the femoral artery proximal to the ligation site of 58, 126 and 194, respectively. Five C57BL/6 mice were additionally measured 4 weeks after occlusion using two repetitions and the visual collateral vessels were assessed for number and location: 2.0 +/- 1.2 in quadriceps muscle, 0.6 +/- 0.5 in adductor (deep adductor vessel), 0.0 +/- 0.0 in adductor (surface adductor vessels). The results showed a significant difference, two-sided t-test, p < 0.05, in number of vessels in all the locations. We have shown that this method can be utilized to elucidate the contribution of collateral vessels to arterial flow., (Copyright 2004 John Wiley & Sons, Ltd.)

We have studied an animal model of acute local inflammation in muscle induced by Aspergillus fumigatus by using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We have compared our data to those found using histopathology and segmentation maps obtained by the mathematical processing of three-dimensional T2-weighted MRI data via a neural network. The MRI patterns agreed satisfactorily with the clinical and biological evidence of the phases of acute local infection and its evolution towards chronicity. The MRS results show a statistically significant increase in inorganic phosphate and a significant decrease in phosphocreatine levels in the inflamed region. Image segmentation made with a self-organizing, neural-network map yielded a set of ordered representatives that remained constant for all animals during the inflammatory process, allowing a non-invasive, three-dimensional identification and quantification of the inflamed infected regions by MRI., (Copyright 2002 John Wiley & Sons, Ltd.)

Background: Verruciform xanthoma (VX) is a rare, benign neoplasm arising predominantly in the oral cavity, but it has been reported to occur on the genital skin and mucosa as well. VX has also been described in association with epidermal nevi and squamous cell carcinoma. Because of the clinical and histologic similarities between VX and condyloma acuminata, and a recent report of HPV 6 in association with VX, we investigated the role of human papilloma virus (HPV) in the development of this entity., Methods: In situ hybridization and a nested PCR approach utilizing degenerate primers were utilized to establish whether HPV infection could be playing a role in the development of the VX., Results: In situ hybridization failed to identify HPV DNA. The highly sensitive nested PCR approach also failed to detect HPV DNA., Conclusions: The failure to detect HPV DNA, even by very sensitive methods, provides strong evidence that our case of VX is not an HPV-induced lesion. A review of other possible etiologies, including alternative infectious agents and genetic associations, are discussed.

Porokeratosis of Mibelli was diagnosed in a 9-year-old Afro-American girl. The lesion was rather large (4.1 x 2.0 cm) and had developed rapidly over the course of six months. Considering the potential for malignant transformation without neglecting the importance of cosmesis, carbon dioxide laser vaporization with curettage was chosen to ablate the lesion. Within two months the entire treated area revealed recurrent porokeratosis. Due to the aggressive nature of this lesion, complete excision was performed.

Congenital giant juvenile xanthogranuloma is an uncommon lesion that apparently has benign biologic behavior in most reported patients. In one of our three patients it was necessary to perform histochemical reactions with CD 1 (-), MAC 387, and electron microscopy to rule out Langerhans cell histiocytosis. The other patients had a typical histologic picture, with foamy histiocytes and Touton cells in association with lymphocytes and eosinophils. Comments about treatment are also made.

A newly described exanthem of infancy consists of an eczematous or scarlatiniform eruption that starts initially from one axillary fold and spreads unilaterally and centrifugally on the trunk and the proximal part of the upper limb. Minor lesions are infrequently present on the contralateral side. The rash may be slightly pruritic and sometimes associated with a moderate regional lymphadenopathy. The appearance in small epidemics and the seasonal prevalence imply a viral agent as the probable origin. We report two new cases of this entity, which appears to be not so rare.

The fiber architecture of adult human sartorius and gracilis muscles was examined using a combination of fiber microdissections and histological methods. Intact fibers were dissected from fascicles of muscle strips that were digested in nitric acid. All of these fibers terminate intrafascicularly by tapering to a fine strand at one or both ends. They measure 4-20 cm after correction for shrinkage. Systematic dissections of 1 cm long blocks sampled at intervals along the muscle length suggest that tapered fiber endings occur at all locations along the muscle but are most common centrally; here they accounted for up to 14% of dissected fibers in each block. Transverse sections of muscle confirm that fiber profiles with small diameters occur at all levels of the muscle but are especially common in sections more than 5 cm from its origin or insertion. The architectural arrangement demonstrated here suggests that long human muscles, like muscles in other species, are composed of relatively short, in-series fibers. This has many implications for the neural activation and force-developing behavior of these muscles that must be considered when paralyzed muscles are reanimated using electrical stimulation. Further, it may predispose long muscles to certain types of neuromuscular damage and dysfunction.

A 6-year-old Caucasian girl had dozens of asymptomatic, flesh-colored, 2- to 5-mm eruptive vellus hair cysts. These papules on the buttocks, thighs, and groin increased in number for three months. Histologic examination revealed poorly defined, keratin-filled cysts in the upper middermis, containing numerous transversely or obliquely cut portions of vellus hair. The histopathologic differential diagnosis with other epithelial cysts containing hair shafts is debated, and new clinical differential diagnoses are proposed. Review of the literature suggests that eruptive vellus hair cyst is not a rare disorder, but its frequency is probably underestimated due to paucity of symptoms. Nevertheless, the clinical relevance of some of the differential diagnoses should convince clinicians to obtain histologic confirmation.

Five cases of a previously undescribed variant of epithelioid sarcoma are presented. This variant differs from the usual lesion in its absence of the typical necrobiotic nodular epithelioid pattern. It is instead composed of deceptively bland fibrohistiocytic and myoid cells arranged in a fibroma-like or dermatofibroma-like pattern with an affinity for osseous involvement. The clinical presentation, ultrastructural features, and presence of vimentin and low molecular weight keratin within the tumor cells justifies their designation as an epithelioid sarcoma variant.

Correlated light and electron microscopic study of four fibrous histiocytomas of proven malignancy has confirmed the presence of histiocyte-like and fibroblast-like cells in this tumor. In addition, an undifferentiated cell type, giant cells, xanthomatous cells, and rare cells with morphological characteristics intermediate between those of histiocytes and fibroblasts were seen. "Nuclear body" type inclusions were commonly present in both principal cell types in all four cases, as were the somewhat less common cytoplasmic inclusion bodies. Electron microscopic study of a tissue culture of one of these tumors demonstrated only fibroblast-like, histiocyte-like, and xanthomatous cells. The possibility is suggested that both principal cell types in this tumor may derive from the same undifferentiated stem cell.

The results of surgical treatment in 40 patients with a soft tissue sarcoma of the thigh were analyzed to determine the influence of the anatomic setting on the effectiveness of the procedure. The anatomic setting, based on functional anatomic compartments, was defined as either intra- or extracompartmental. The lesions were graded for aggressiveness as either high or low. The lesions were staged by biologic aggressiveness, anatomic setting, and metastases. The procedures, whether amputations or local resections, were classified by the relationship of the surgical margin to the pseudocapsule and reactive zone about the lesion as marginal, wide, or radical. Marginal procedures were done four times with two recurrences. Wide margins were achieved 12 times. When done for low grade lesions, there were no recurrences (0/2), but when done for high grade lesions, the recurrence rate was 30% (3/10). Radical margins were obtained 24 times. There was one recurrence after a radical procedure. Recurrence rates did not depend upon whether the procedure was a resection or amputation but upon the margin achieved. The anatomic setting of the lesion was intracompartmental in 13 cases and extracompartmental in 27. Not only were surgically adequate margins achieved more often for intracompartmental lesions (10/13) than for extracompartmental lesions (17/27), but there was a significant difference in the manner required to achieve an adequate margin. Although 9 of the 13 intracompartmental lesions were amenable to nonablative resection, only 3 of 27 extracompartmental lesions were resectable. The margin required for local control (wide vs. radical) was dictated by the biologic aggressiveness (grade) of the lesion. How the necessary margin was most satisfactorily achieved (resection vs. amputation) was determined by the anatomic setting (intra- vs. extracompartmental).