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Dermoid cysts rarely present in the retroperitoneal space or during adulthood. In this case report, we describe the clinical presentation, operative and post-operative course of a 31-year old with a retroperitoneal dermoid cyst. The patient presented with buttock and leg pain/paresthesia found to have a retroperitoneal mass between the psoas muscle and L5/S1 disk space. We describe the operative approach, including intra-operative images, of the resection by a team of urologists and neurosurgeons. The histology is also presented. Finally, we discuss the benefits of use of intra-operative ultrasound and neuromonitoring.

ObjectivesSoft tissue sarcomas are a group of tumors derived from the mesenchymal origin. Historically, they have been classified according to morphologic and immunohistochemical characteristics. The advent of multiplexed next-generation sequencing (NGS), specifically RNA sequencing, has modified the classification of such tumors and others by determining categorization based on molecular alterations. The NUTM1 rearrangement, previously thought to be present only in carcinomas, has recently been reported in poorly differentiated high-grade sarcomas of the soft tissue. We present the first reported case of an epithelioid hyalinizing sarcoma harboring the MGA-NUTM1 fusion in an acral site.MethodsHistopathologic, immunohistochemical, and molecular testing were performed on resection tissue.ResultsHistologically, the tumor showed an epithelioid morphology with prominent background hyalinization. Immunohistochemically, the tumor expressed CD99 and nuclear NUT-1. By NGS the tumor harbors MGA-NUTM1 fusion.ConclusionsOur findings support more extensive use of NGS for accurate sarcoma classification and identification of potential therapeutic targets. Furthermore, they corroborate the fact that NUTM1-rearranged soft tissue tumors represent a spectrum of heterogeneous morphologic entities. This case also highlights the utility of NUT-1 immunohistochemical study as a possible screening tool for NUTM1-fused sarcomas.

Objectives To characterize the expression of SOX11 and TFE3 proteins in solid-pseudopapillary neoplasms (SPNs) and their histologic mimickers. Methods Immunohistochemistry for SOX11, TFE3, and β-catenin was performed on 31 cases of surgically resected SPNs. Neuroendocrine tumors, acinar cell carcinomas, and pancreatoblastomas served as controls. Results Nuclear immunoreactivity for SOX11 was detected in all SPNs and five of 31 control tumors. Nuclear immunoreactivity for TFE3 was detected in 30 SPNs and three control tumors. Nuclear immunoreactivity for β-catenin was detected in all SPNs and four control tumors. The combination of three markers as immunohistochemical panels resulted in optimal sensitivity and specificity. Conclusions Both SOX11 and TFE3 were overexpressed in SPNs and may be involved in the pathogenesis. Clinically, SOX11 and TFE3 can be potentially used as diagnostic markers in distinguishing indeterminate SPNs from their histologic mimickers.

We evaluated hepatocyte paraffin 1 (HepPar1) antigen expression, a sensitive marker of small intestinal differentiation, in combination with morphologic features to demonstrate intestinal differentiation in cases equivocal for Barrett esophagus (BE). Clinicopathologic features and HepPar1 expression were recorded for 54 BE cases, 45 consistent with reflux esophagitis (RE) cases, and 65 “suspicious” for BE (SBE) cases. The SBE category included RE cases with 2 or more morphologic changes associated with BE or metaplastic reaction to injury (eg, multilayered epithelium, squamous islands, goblet cell mimickers, pancreatic metaplasia). HepPar1 was expressed in all 54 BE cases, 4 of 45 RE cases, and 24 of 65 SBE cases. In SBE cases, 2 or more morphologic changes were associated with HepPar1 expression in 37% of cases (24/65), 3 or more features in 59% (13/22), and 4 or more features in 100% (4/4) (P ≤ .004). The combination of certain morphologic changes and HepPar1 expression in clinically suspicious distal esophageal biopsy cases without goblet cells supports the presence of evolving intestinal metaplasia.

It is estimated that 35% of total hip arthroplasties (THAs) involve a second-generation metal-onmetal (MOM) prosthesis. A novel complication has appeared in a subset of patients with MOM THAs that is described as an aseptic, lymphocyte-dominated vasculitis-associated lesion (ALVAL). The clinical features of ALVAL are nonspecific, but patients complain of pain and may develop “pseudotumors.” It is hypothesized that metal ions are released from the prosthesis and form haptens with native proteins that elicit a type IV hypersensitivity response in the local soft tissues. Histopathologic descriptions of ALVAL are similar to those of failed arthroplasty in general, with the addition of a dense perivascular inflammatory infiltrate that is the hallmark of ALVAL. We report 3 cases of ALVAL with clinical, radiographic, and histologic findings. Accurate assessment is crucial because an intraoperative diagnosis of chronic inflammation suggestive of ALVAL will necessitate a replacement of the prosthetic component surfaces. Hip arthroplasty is a common procedure used to alleviate pain and dysfunction associated with a variety of joint problems, the most common being degenerative joint disease. It is estimated that the number of people undergoing hip replacement more than doubled in the interval between 1990 and 2002. 1 As the incidence of primary hip arthroplasty has increased dramatically during the last several years, so too has the need for revision of older prostheses. It is estimated that the number of procedures will increase to substantially more than 500,000 primary hip arthroplasty procedures and almost 100,000 revisions annually within the next 20 years. 2