Atypical Spindle Cell/Pleomorphic Lipomatous Tumor With Sarcomatous Transformation: Clinicopathologic and Molecular Analysis of 4 Cases.

Atypical spindle cell/pleomorphic lipomatous tumor (ASPLT) is a recently described adipocytic tumor predominantly affecting the subcutaneous soft tissues of adults. Previous studies have shown that ASPLT follows a benign clinical course with a 4% to 12% local recurrence rate and no risk of dedifferentiation. Herein, we describe the clinicopathologic and molecular findings of 4 cases of ASPLT showing unequivocal sarcomatous transformation. Three patients were male and one was female, aged 65, 70, 74, and 78 years. Two cases presented as mass-forming lesions, while 1 case was incidentally discovered. The tumors measured 30, 55, 80, and 110 mm and occurred in the chest wall (n = 2) or arm (n = 2); all were subcutaneous. Microscopically, they showed a biphasic appearance comprising a low-grade ASPLT component and a high-grade sarcomatous component. The low-grade components showed features in the spectrum of either atypical pleomorphic lipomatous tumor (n = 2) or atypical spindle cell lipomatous tumor (n = 2). The high-grade components displayed leiomyosarcoma-like (n = 2), pleomorphic liposarcoma-like (n = 1) or undifferentiated sarcoma-like (n = 1) morphology. On immunohistochemistry, tumors were negative for MDM2 and showed loss of RB1 expression. In addition, the leiomyosarcoma-like areas seen in 2 cases were positive for smooth muscle actin and H-caldesmon. Single-nucleotide polymorphism array, performed in 3 cases, showed deletions of TP53, RB1, and flanking genes in both components. In contrast, the sarcomatous components showed more complex genomic profiles with rare segmental gains and recurrent loss of PTEN (n = 3), ATM (n = 2), and CDKN2A/B (n = 2) among other genes. Whole exome sequencing identified a TP53 variant in one case and an ATRX variant in another, each occurring in both tumor components. Limited clinical follow-up showed no recurrence or metastasis after 1 to 13 months (median, 7.5 months) postsurgical excision. Altogether, our data support that ASPLT can rarely develop sarcomatous transformation and offer insights into the molecular mechanisms underlying this event.

MDM4 amplification in atypical lipomatous tumors/well-differentiated liposarcoma: Private event or alternative oncogenic mechanism?

Adipocytic tumors are the most common mesenchymal tumors in soft tissues. Among them, a diagnostic challenge relies in the distinction between lipoma and atypical lipomatous tumor (ALT)/well differentiated liposarcoma (WDLPS), as both entities are often undistinguishable not only from a radiological point of view, but also at the microscopic level and particularly when dealing with small tumor specimen. Thus, detection of recurrent MDM2 amplifications may be the only criteria to discriminate malignant tumors from lipomas. In this study, we report the case of a patient diagnosed with a well differentiated, adipocytic tumor located in the inferior limb and lacking MDM2 amplification, whose diagnosis was reclassified for ALT/WDLPS after identification of an alternative MDM4 amplification by comparative genomic hybridization profiling, whole exome sequencing and fluorescence in situ hybridization (FISH). Screening of a cohort of 37 large, deep-seated, well-differentiated adipocytic tumors previously classified as lipomas using RT-qPCR and FISH failed to detect other cases of MDM4-amplified ALT/WDLPS. This report shows that MDM4 amplification is an exceptional molecular event alternative to MDM2 amplification in ALT/WDLPS. This alteration should be considered and looked for in suspicious adipocytic tumors to optimize their surgical management.

Lipoblastoma-Like Tumor and Fibrosarcoma-Like Lipomatous Neoplasm Represent the Same Entity: A Clinicopathologic and Molecular Genetic Study of 23 Cases Occurring in Both Men and Women at Diverse Locations.

Lipoblastoma-like tumor (LLT) is a benign soft tissue tumor demonstrating mixed morphologic features of lipoblastoma, myxoid liposarcoma, and spindle cell lipoma but lacking genetic alterations associated with those tumors. LLT was originally thought to be specific to the vulva but has since been reported in the paratesticular region. The morphologic features of LLT overlap with those of "fibrosarcoma-like lipomatous neoplasm" (FLLN), a rare, indolent adipocytic neoplasm considered by some to form part of the spectrum of atypical spindle cell and pleomorphic lipomatous tumor. We compared the morphologic, immunohistochemical, and genetic features of 23 tumors previously classified as LLT (n = 17) and FLLN (n = 6). The 23 tumors occurred in 13 women and 10 men (mean age, 42 years; range, 17 to 80 years). Eighteen (78%) cases arose in the inguinogenital region, whereas 5 tumors (22%) involved noninguinogenital soft tissue, including the flank (n = 1), shoulder (n = 1), foot (n = 1), forearm (n = 1), and chest wall (n = 1). Microscopically, the tumors were lobulated and septated, with variably collagenized fibromyxoid stroma, prominent thin-walled vessels, scattered univacuolated or bivacuolated lipoblasts, and a minor component of mature adipose tissue. Using immunohistochemistry, 5 tumors (42%) showed complete RB1 loss, with partial loss in 7 cases (58%). RNA sequencing, chromosomal microarray, and DNA next-generation sequencing study results were negative for significant alterations. There were no clinical, morphologic, immunohistochemical, or molecular genetic differences between cases previously classified as LLT or FLLN. Clinical follow-up (11 patients [48%]; range, 2-276 months; mean, 48.2 months) showed all patients were alive without disease, and only one patient had experienced a single local recurrence. We conclude that LLT and FLLN represent the same entity, for which "LLT" seems most appropriate. LLT may occur in either sex and any superficial soft tissue location. Careful morphologic study and appropriate ancillary testing should allow for the distinction of LLT from its potential mimics.

Radiomics-based approaches outperform visual analysis for differentiating lipoma from atypical lipomatous tumors: a review.

BACKGROUND: Differentiating atypical lipomatous tumors (ALTs) and well-differentiated liposarcomas (WDLs) from benign lipomatous lesions is important for guiding clinical management, though conventional visual analysis of these lesions is challenging due to overlap of imaging features. Radiomics-based approaches may serve as a promising alternative and/or supplementary diagnostic approach to conventional imaging. PURPOSE: The purpose of this study is to review the practice of radiomics-based imaging and systematically evaluate the literature available for studies evaluating radiomics applied to differentiating ALTs/WDLs from benign lipomas. REVIEW: A background review of the radiomic workflow is provided, outlining the steps of image acquisition, segmentation, feature extraction, and model development. Subsequently, a systematic review of MEDLINE, EMBASE, Scopus, the Cochrane Library, and the grey literature was performed from inception to June 2022 to identify size studies using radiomics for differentiating ALTs/WDLs from benign lipomas. Radiomic models were shown to outperform conventional analysis in all but one model with a sensitivity ranging from 68 to 100% and a specificity ranging from 84 to 100%. However, current approaches rely on user input and no studies used a fully automated method for segmentation, contributing to interobserver variability and decreasing time efficiency. CONCLUSION: Radiomic models may show improved performance for differentiating ALTs/WDLs from benign lipomas compared to conventional analysis. However, considerable variability between radiomic approaches exists and future studies evaluating a standardized radiomic model with a multi-institutional study design and preferably fully automated segmentation software are needed before clinical application can be more broadly considered.

Angiolipoma: a review of 778 lesions in 344 patients.

BACKGROUND: Angiolipomas are benign subcutaneous nodules that are commonly multifocal and easily overlooked by those not familiar with their appearance. The objective of this study was to identify the spectrum of the clinical and imaging features of this lesion, to include MR, CT, and US features. METHODS: A retrospective review of our institutional pathology database for biopsy-proven cases of angiolipoma between January 1, 2019, through December 31, 2021, was done. We identified 334 patients who underwent surgical resection of 788 individual lesions. MR imaging studies were available in 43 cases, CT in 39 cases, and ultrasound imaging in 72 cases. Clinical features (patient age, gender, surgical indication, number of lesions) were reviewed. Imaging feature analysis included the anatomic location, content of fat, vascularity, and modality-specific imaging features. RESULTS: All 778 angiolipomas were located in the subcutaneous tissues (median size, 2.4 cm, range 0.4-7.7 cm), with over 51% located in the upper extremity. The most common presentation was a symptomatic mass or slowly growing symptomatic mass. Imaging showed a subcutaneous lesion with a lobulated bean shape, which typically abutted the skin. Intralesional fat was identified in 85% of lesions on CT and MRI. Vessels were commonly seen on CT and MR, with enhancement best seen on MR. On US, lesions were heterogeneous and mildly hyperechoic, most often with no identifiable vascularity. CONCLUSION: Angiolipomas typically have characteristic imaging features. Awareness of this diagnosis and the spectrum of its imaging features is important and can facilitate a definitive diagnosis.

Multimodality imaging features of parosteal lipomas.

OBJECTIVE: To examine the multimodality imaging characteristics of parosteal lipomas. MATERIALS AND METHODS: With IRB approval, our institutional imaging database and medical record were retrospectively reviewed from 1990-2020 for cases of pathologically-proven and/or imaging diagnosed parosteal lipomas. RESULTS: There were 22 patients (12 males, 10 females) with a mean age of 57.1 ± 12.7 years (range 31-80 years). 11/22 cases (50%) were pathologically-confirmed on biopsy or surgical resection and 11/22 (50%) had imaging features compatible with parosteal lipoma. Lesions occurred most commonly along the femur (8/22, 36%), followed by the forearm (3/22, 14%). All cases demonstrated a juxtacortical fatty mass containing an osseous excrescence that was firmly attached to the cortical surface. The osseous excrescences were characterized as pedunculated in 16/22 (73%) and sessile in 6/22 (27%). The average largest dimension of the osseus excrescences was 2.4 ± 1.6 cm (range 0.8-6.1 cm) and the lipomatous portions 7.8 ± 3.8 cm (range 2.0-19.5 cm). The excrescences contained mature bone in 12/22 (55%) cases and a mixture of mature bone and radiating bone spicules in 10/22 (45%). There were non-lipomatous elements in the fatty portion of the mass in 13/22 (59%) of cases. Most cases (19/22, 85%) had cortical thickening/periostitis near the base of the osseous stalk. Two patients had a bone scan that demonstrated uptake in the osseous excrescence, and two patients had an FDG PET/CT that demonstrated no uptake. CONCLUSION: Parosteal lipomas are a rare benign lipomatous tumor with pathognomonic multimodality imaging features that may obviate the need for biopsy.

Bone and soft tissue tumors at the borderlands of malignancy.

This review examines findings of musculoskeletal neoplasms whose equivocal imaging and/or histopathologic features make it difficult to determine if they will show aggressive behavior. We include both intermediate tumors as defined by the World Health Organization (WHO), and a single low-grade malignancy, low-grade central osteosarcoma, which mimics a benign lesion on imaging and histology. Intermediate tumors are a broad category and are subdivided into tumors that have risk of local recurrence only, and ones that have a risk of distant limb and pulmonary metastases. Difficult intermediate musculoskeletal lesions include atypical cartilaginous tumor/grade 1 chondrosarcoma, atypical lipomatous tumor/grade 1 liposarcoma, and solitary fibrous tumor. We review diagnostic criteria, differential diagnosis, and recommendations for surveillance.

Histopathologic and genetic findings in atypical spindle cell/pleomorphic lipomatous tumors and atypical pleomorphic fibromas.

BACKGROUND: Spindle cell lipomas, pleomorphic lipomas (SCL/PLs), and pleomorphic fibromas (PF) are tumors with loss of retinoblastoma (RB). The latest World Health Organization classification includes a category of atypical spindle cell/pleomorphic lipomatous tumors (ASPLT), which encompasses tumors in this spectrum that show atypical histopathologic features. We have observed PFs that show similar atypical features. METHODS: Cases of SCL/PL and PF with atypical features were collected from tissue archives between 2010 and 2019. Genetic alterations were investigated using array comparative genomic hybridization (aCGH). RESULT: Of 15 cases found, most tumors were dermal based with fibrocytic or fibroadipocytic appearance and occasional lipoblasts. All cases had a high proliferation index with atypical mitotic figures in 71% of cases. Chromosome 13q loss was present in all cases with CGH data. Additional recurrent chromosomal losses included 17p, 16q, 17q, 20p, 4, and 10. No recurrence was found in limited follow-up. CONCLUSIONS: ASPLTs are characterized by loss of RB, prominent nuclear pleomorphism, mitotic activity including atypical mitotic figures, and genomic instability with multiple chromosomal aberrations. A similar group of tumors with these histopathologic features lacks lipomatous differentiation, and we propose the diagnosis of atypical PF as a fibromatous variant of ASPLT. Limited clinical follow-up appears benign.

Can homogeneous, lipomatous tumors be primarily resected without biopsy? A retrospective analysis of 240 tumors.

BACKGROUND: According to guidelines, every soft tissue tumor (STT) larger than 3 cm should be biopsied before definitive resection. Advances in magnetic resonance imaging (MRI) improve the possibility to give a provisional diagnosis of the tumor's entity. Can lipomas and atypical lipomatous tumors (ALTs) of the extremities therefore be primarily marginally resected based on interpretation of MR images without a previous biopsy?. METHODS: In this retrospective, single-center study, 240 patients with the suspicion of a lipomatous tumor in MRI and surgical treatment in our institution between 2011 and 2020 were included. MR imaging was performed before surgery. All resected specimens underwent histopathological analysis. RESULTS: The collective comprised 142 tumors that were suspected as lipoma or ALT by the radiologist and underwent primary marginal resection (PMR). One case had myxoid liposarcoma that was underestimated on MRI and needed radical follow-up resection. One-hundred forty-one patients were cured after PMR. Ninety-eight patients were biopsied initially and in 93 cases resected afterwards according to the necessary oncological margins. CONCLUSION: In our institution, PMR is performed if a lipoma or ALT is suspected on MR imaging. Our treatment method and the diagnostic algorithm are presented. Primary resection spares patients from one surgical procedure, but a slight risk for underestimation of the tumor remains.

Atypical Pleomorphic Lipomatous Tumor of the Right Hand Mimicing Venous Malformation.

We present the case of a 31-year-old woman who was referred with a 12-month history of a tumor on the ulnar side of her dominant right hand. The eventual histopathologic diagnosis was an atypical pleomorphous lipomatous tumor, an entity that has only been recently classified in the World Health Organization Classification of Soft Tissue and Bone Tumors.

MRI findings to differentiate musculoskeletal dedifferentiated liposarcoma from atypical lipomatous tumor.

OBJECTIVE: This study aimed to assess the efficacy of using MRI findings for differentiating musculoskeletal dedifferentiated liposarcoma (DDLP) from atypical lipomatous tumor (ALT). MATERIALS AND METHODS: This study included 22 patients with histopathologically proven DDLP and 35 with ALT in the musculoskeletal areas. All DDLPs were immunohistochemically positive for MDM2. MRI findings for both pathologies were retrospectively reviewed and compared. RESULTS: The maximum lesion diameter was significantly lower in DDLPs than in ALTs (p < 0.01). Ill-defined margin, peritumoral edema, and tail sign were more frequently observed in DDLPs than in ALTs (p < 0.01, respectively). The fatty component was less frequently observed in DDLPs than in ALTs (27 vs. 100%; p < 0.01), whereas the non-fatty component was more frequently observed in DDLPs than in ALTs (100 vs. 11%; p < 0.01). The occupation rate by non-fatty components was significantly higher in DDLPs than in ALTs (p < 0.01). No significant differences were observed in imaging findings associated with fatty component; however, necrosis within the non-fatty component on the contrast-enhanced image was more frequently observed in DDLPs than in ALTs (72 vs. 0%, p < 0.05). CONCLUSION: DDLPs always had a non-fatty component, whereas ALTs always had fatty component. Ill-defined margin, peritumoral edema, tail sign, and necrosis within non-fatty components were useful MRI features for differentiating musculoskeletal DDLP from ALT.

Do contrast-enhanced and advanced MRI sequences improve diagnostic accuracy for indeterminate lipomatous tumors?

PURPOSE: Benign, intermediate-grade and malignant tumors sometimes have overlapping imaging and clinical characteristics. The purpose of this study was to evaluate the added value of contrast-enhanced sequences (dynamic contrast enhancement (DCE)), diffusion-weighted imaging (DWI), and chemical shift imaging (CSI) to noncontrast MRI sequences for the characterization of indeterminate lipomatous tumors. MATERIALS AND METHODS: Thirty-two consecutive patients with histologically proven peripheral lipomatous tumors were retrospectively evaluated. Two musculoskeletal radiologists recorded the MRI features in three sessions: (1) with noncontrast T1-weighted and fluid-sensitive sequences; (2) with addition of static pre- and post-contrast 3D volumetric T1-weighted sequences; and (3) with addition of DCE, DWI, and CSI. After each session, readers recorded a diagnosis (benign, intermediate/atypical lipomatous tumor (ALT), or malignant/dedifferentiated liposarcoma (DDL)). Categorical imaging features (presence of septations, nodules, contrast enhancement) and quantitative metrics (apparent diffusion coefficient values, CSI signal loss) were recorded. RESULTS: For 32 tumors, the diagnostic accuracy of both readers did not improve with the addition of contrast-enhanced sequences, DWI, or CSI (53% (17/32) session 1; 50% (16/30) session 2; 53% (17/32) session 3). Noncontrast features, including thick septations (p = 0.025) and nodules ≥ 1 cm (p < 0.001), were useful for differentiating benign tumors from ALTs and DDLs, as were DWI (p = 0.01) and CSI (p = 0.009) metrics. CONCLUSION: The addition of contrast-enhanced sequences (static, DCE), DWI, and CSI to a conventional, noncontrast MRI protocol did not improve diagnostic accuracy for differentiating benign, intermediate-grade, and malignant lipomatous tumors. However, we identified potentially useful imaging features by DCE, DWI, and CSI that may help distinguish these entities.

Atypical spindle cell/pleomorphic lipomatous tumor with a sarcomatous component showing high mitotic activity and Ki-67 labeling index: report of a unique case mimicking dedifferentiated liposarcoma.

Atypical spindle cell/pleomorphic lipomatous tumor (ASPLT) is a new entity of benign adipocytic tumor that spans a wide spectrum of histology from adipocytic to spindle cell/pleomorphic tumors. The latter non-adipocytic component rarely shows sarcomatous features although ASPLTs are not thought to dedifferentiate. A 78-year-old woman with ASPLT in the left thigh had a sarcomatous component with high mitotic activity and Ki-67 labeling index (LI) mimicking dedifferentiated liposarcoma. The adipocytic component consisted of various-sized adipocytic cells with few lipoblasts. The sarcomatous component consisted of a fascicular proliferation of atypical spindle cells with scattered large bizarre and multinucleated giant cells. Mitotic figures including atypical mitoses were frequently observed. Immunohistochemically, the tumor cells were positive for cluster of differentiation 34 but not mouse double minute 2 homolog (MDM2), cyclin-dependent kinase 4 (CDK4), or retinoblastoma (Rb) protein. Ki-67 LI in the sarcomatous component reached 40%. MDM2 and CDK4 genes were not amplified and 13q14 including the RB1 locus was deleted according to fluorescence in situ hybridization. The patient is alive with no evidence of local recurrence or distant metastasis 3.5 years after surgery. As ASPLT may exhibit morphological variation, it is important to rule out dedifferentiated liposarcoma with careful pathological examination.

Subcutaneous shoulder hibernoma presenting as an atypical lipomatous tumor - a case report.

Hibernomas are soft tissue tumors derived from remnants of brown fat. They are rare masses that can have variable presentations ranging from incidental asymptomatic masses to pain due to nerve compression. We present the case of a 52-year-old male presenting with an atypical lipomatous mass on ultrasound and magnetic resonance imaging. The mass was excised and sent for pathology with the result being a hibernoma. We should be vigilant in the treatment of such tumor presentations as they may be a low grade liposarcoma in disguise. Surgical biopsy or excision is the best treatment for achieving a definite diagnosis.

Image-Guided Core Needle Biopsy of Adipocytic Tumors: Diagnostic Accuracy and Concordance With Final Surgical Pathology.

OBJECTIVE. Diagnostic accuracy of core needle biopsy (CNB) for adipocytic tumors can be low because of sampling error from these often large, heterogeneous lesions. The purpose of this study was to evaluate the diagnostic accuracy of image-guided CNB for various adipocytic tumors in comparison with excisional pathology. MATERIALS AND METHODS. Adipocytic tumors (n = 77) of all adult patients undergoing image-guided CNB and subsequent surgical excision of an adipocytic tumor at a tertiary referral center between 2005 and 2019 were studied. To determine concordance, we compared pathologic diagnoses based on CNB to the reference standard of pathologic diagnoses after surgical excision. Tumors were divided into three categories (benign lipomatous tumors [lipoma, lipoma variants, hibernomas], atypical lipomatous tumors [ALTs] or well-differentiated liposarcomas [WDLs], and higher grade liposarcomas [myxoid, dedifferentiated, pleomorphic]), and diagnostic accuracy was calculated for each category. RESULTS. In 73 of 77 adipocytic tumors (95%), diagnosis at CNB and diagnosis after excision were concordant. Accuracy of diagnosis was poorer for ALTs and WDLs than for the other two categories, and the difference was statistically significant (p < .002). For the 29 benign lipomatous tumors and the 27 higher-grade liposarcomas, diagnoses at CNB and after excision were concordant in all cases (100%). Seventeen of the 21 tumors (81%) diagnosed as ALTs or WDLs at CNB had a concordant diagnosis after excision; four of the 21 were upgraded (dedifferentiated liposarcoma, n = 3; myxoid liposarcoma, n = 1). CONCLUSION. CNB provides high diagnostic accuracy for adipocytic tumors, particularly for benign lipomatous tumors and higher grade liposarcomas. However, though still high at 81%, diagnostic accuracy of CNB is not as high for tumors diagnosed as ALTs or WDLs. Awareness of this limitation is important when determining management, particularly of cases of ALT or WDL for which surgery is not planned.

Surgical excision of a rare cardiac tumor: Cardiac hibernoma.

BACKGROUND AND AIM: Cardiac hibernoma is a very rare benign cardiac tumour. We report a case of its surgical management. METHODS: A case study with retrospective review of prospective patient data. RESULTS: A 60 year old male who presented with acute shortness of breath was found to have SVC compression on cardiac imaging. At operation the tumour was in the right atrial wall invading the intra-atrial groove and extending over superior vena cava (SVC), causing significant symptoms of SVC obstruction and tamponade. This was resected and the right atrium was reconstructed with Bovine pericardial patch. He was discharged home well. CONCLUSIONS: Cardiac hibernoma is a rare tumour which can be successfully treated by surgical excision.

Recent Advancement in Atypical Lipomatous Tumor Research.

After Evans and colleagues identified the lipomatous tumor with a well-differentiated liposarcoma in a subcutaneous location or within a muscle layer, namely, atypical lipomatous tumor (ALT), this malignancy has been investigated to clarify the characteristics of clinical behavior and genomic changes. As one of the important issues for clinicians, it is a hot topic of how to distinguish ALT from benign lipoma in the clinical aspect. Recent studies revealed novel findings to clarify the risk factor for the diagnosis of ALT and molecular targets for the treatment of ALT. Clinical characteristics of superficial-type ALT well reflect the subcutaneous location of the tumor and are slightly different compared to deep-type ALT, such as tumor size. In addition, there has been a recent discovery of novel findings in ALT-related genes, namely, HMG2A (high mobility group protein 2a), YEATS4 (YEATS domain containing 4), and CPM (Carboxypeptidase M). Recent updates on treatment for advanced ALT are well developed including immunotherapy and conducting clinical trials. Finally, this review introduces one of the hot topics of ALT research focused on epigenetic changes: their attention in recent updates on clinical characteristics and the novel discovery of related genes, treatment, and epigenetic modifications in atypical lipomatous tumors.

Lipomatous Soft Tissue Masses: Challenging the Paradigm of Routine Preoperative Biopsy.

BACKGROUND: Lipomatous masses are the most common soft tissue tumors. While the majority are benign lipomas, it is important to identify those masses that are malignant prior to excision. Current guidelines recommend core needle biopsy (CNB) for all lipomatous masses larger than 3-5 cm. The objective of this study was to determine if routine preoperative CNB based on mass size is necessary, or if radiographic features can guide the need for CNB. MATERIALS AND METHODS: Patients who underwent excision of extremity or truncal lipomatous masses at a single institution from October 2014 to July 2017 were retrospectively reviewed. By protocol, preoperative imaging was routinely obtained for all masses larger than 5 cm. High-risk radiographic features (intramuscular location, septations, nonfat nodules, heterogeneity, and ill-defined margins) and surgical pathology were evaluated to determine patients most likely to benefit from preoperative CNB. RESULTS: Of 178 patients, 2 (1.1%) had malignant tumors on surgical pathology. All masses smaller than 5 cm were benign and, if imaging was obtained, had two or fewer high-risk radiographic features. Both of the patients with malignant tumors had masses larger than 5 cm, preoperative imaging that showed at least four high-risk radiographic features, and underwent CNB prior to excision. CONCLUSIONS: The overall rate of malignancy is very low. The results of this study suggest that lipomatous masses smaller than 5 cm without concerning clinical characteristics do not require preoperative imaging or CNB. Conversely, lipomatous masses larger than 5 cm should undergo routine MRI with subsequent CNB if multiple high-risk radiographic features are present.

Low-grade Osteosarcomatous Dedifferentiation of an Atypical Lipomatous Tumor in a Pediatric Patient.

Atypical and malignant lipomatous tumors are infrequent in the pediatric population. Within this uncommon cohort, the morphologically and genetically related spectrum of atypical lipomatous tumor/well-differentiated liposarcoma/dedifferentiated liposarcoma (ALT/WDL/DDLS) is markedly rare. Their shared characteristic molecular aberration is a genomic amplicon of a region of chromosome 12q, including the oncogenes MDM2 and CDK4. We present an unusual case of a pediatric patient with an ALT, with recurrence after 2 years in the form of a bone-forming mass, radiologically and pathologically mimicking parosteal osteosarcoma, a tumor also molecularly characterized by amplification of MDM2 and CDK4. However, with ample histologic sampling, a single focus of lipogenic differentiation was identified, thus representing the first near complete low-grade osteosarcomatous dedififferentation reported within ALT/WDL/DDLS and the first ever in pediatric patient. The case serves a reminder of a diagnosis differential and pitfalls within MDM2-amplified tumors.

Qualitative evaluation of MRI features of lipoma and atypical lipomatous tumor: results from a multicenter study.

OBJECTIVES: The objectives of the study are (1) to distinguish lipoma (L) from atypical lipomatous tumor (ALT) using MRI qualitative features, (2) to assess the value of contrast enhancement, and (3) to evaluate the reproducibility and confidence level of radiological readings. MATERIALS AND METHODS: Patients with pathologically proven L or ALT, who underwent MRI within 3 months from surgical excision were included in this retrospective multicenter international study. Two radiologists independently reviewed MRI centrally. Impressions were recorded as L or ALT. A third radiologist was consulted for discordant readings. The two radiologists re-read all non-contrast sequences; impression was recorded; then post-contrast images were reviewed and any changes were recorded. RESULTS: A total of 246 patients (135 females; median age, 59 years) were included. ALT was histopathologically confirmed in 70/246 patients. In multivariable analysis, in addition to the lesion size, deep location, proximal lower limb lesions, demonstrating incomplete fat suppression, or increased architectural complexity were the independent predictive features of ALT; but not the contrast enhancement. Post-contrast MRI changed the impression in a total of 5 studies (3 for R1 and 4 for R2; 2 studies are common); all of them were incorrectly changed from Ls to ALTs. Overall, inter-reader kappa agreement was 0.42 (95% CI 0.39-0.56). Discordance between the two readers was statistically significant for both pathologically proven L (p < 0.001) and ALT (p = 0.003). CONCLUSION: Most qualitative MR imaging features can help distinguish ALTs from BLs. However, contrast enhancement may be limited and occasionally misleading. Substantial discordance on MRI readings exists between radiologists with a relatively high false positive and negative rates.