PET evaluation of fatty tumors in the extremity: possibility of using the standardized uptake value (SUV) to differentiate benign tumors from liposarcoma

An Atypical Spindle Cell/Pleomorphic Lipomatous Tumor of the Thigh With a Difficult Imaging Diagnosis That Mimicked a Malignant Lipomatous Tumor

ABSTRACT

Atypical spindle cell/pleomorphic lipomatous tumor is categorized as a benign lipomatous tumor, but various MRI findings pose accurate diagnostic challenges. In our case, both MRI and PET/CT scans indicated the possibility of atypical lipomatous tumor/well-differentiated liposarcoma or dedifferentiated liposarcoma. Needle biopsy suggested benign to low-grade malignancy; hence, we opted for the wide resection. The final diagnosis of atypical spindle cell/pleomorphic lipomatous tumor was confirmed through histopathology analysis, including immunohistochemistry and fluorescence in situ hybridization. Since achieving an accurate diagnosis solely through imaging can be challenging, histopathology remains essential.

Primary renal myxoid liposarcoma with pancreatic invasion on 18F-FDG PET/CT: first case report and literature review

Background

Myxoid liposarcoma (MLS) is a rare malignant soft tissue sarcoma that predominantly manifests in the deep soft tissues of the extremities, particularly within the musculature of the thigh. Unlike other types of liposarcoma, MLS demonstrates a propensity for metastasis to atypical sites, including the lung parenchyma, soft tissues, retroperitoneum, mediastinum, breast, liver, thymus, lymph nodes, and bones. The definitive diagnosis primarily relies on histology with HE staining. Imaging modalities such as ultrasound, CT, MRI, and 18F-FDG PET/CT scans serve as valuable tools for tumor identification.

Case report

A 57-year-old man presented with symptoms of abdominal distention and vomiting 1 month ago. Contrast-enhancement CT revealed a heterogeneous hypodense mass in the upper-middle part of the left kidney, displaying irregular morphology and protrusion towards the exterior of the kidney, with abundant blood supply and had a maximum dimension of approximately 10.7 cm × 9.0 cm. Additionally, a rounded soft tissue density was identified in the pancreatic body. Multiplanar reconstruction demonstrated a connection between the pancreatic lesion and the kidney mass. 18F-FDG PET/CT was conducted for staging, revealing significant growth of the lesion in the upper-middle part of the left kidney, extending beyond the kidney and infiltrating the pancreatic body. The lesion demonstrated remarkably high 18F-FDG uptake (SUVmax = 10.2, MTV = 136.13 cm3, TLG = 484.62). The postoperative pathological examination confirmed the diagnosis of MLS. On the 10th day post-surgery, the patient presented with tumor recurrence and underwent another surgical resection. Unfortunately, during the operation, the patient experienced a sudden cardiac arrest and died.

Conclusion

Renal MLS with invasion into the pancreas is very rare in clinical practice. Due to the limited research on the utilization of 18F-FDG PET/CT in this particular context, given the rarity and low incidence of MLS, its role remains largely unexplored. As PET/CT imaging becomes increasingly prevalent, thorough imaging of disease sites becomes indispensable for the development of treatment protocols and the monitoring of treatment response.

The Usefulness of Short-Interval Sequential FDG PET/CT Studies in Defining the Benignity of Hypermetabolic Lipomatous Tumor

ABSTRACT

We present an interesting case of incidentally detected lipomatous tumor in an oncological patient that could result in a false-positive interpretation by exhibiting intense FDG activity similar to that of a malignant neoplasm. Careful evaluation of FDG uptake changes on sequential short-interval PET/CT studies was helpful in defining the benign nature of the tumor as the hypermetabolism was gradually disappearing obviating the need for a major surgery.

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.

Omental lipoma: a rare cause of a giant intra-abdominal mass

Primary tumors of the omentum, let alone omental lipomas, are rare causes of a large intra-abdominal mass. We report a case of an adult male presenting with an intra-abdominal mass, representative of a giant omental lipoma radiologically, confirmed on histopathology after complete resection at laparotomy. The case highlights the preoperative workup of a suspected omental lipoma, including the utility of various radiological modalities in differentiating from malignant pathologies, and anatomical characterization of the lesion for surgical planning.

FDG PET/CT in Dendritic Fibromyxolipoma of the Thigh

ABSTRACT

Dendritic fibromyxolipoma is a rare recently described benign soft tissue tumor, which may be misinterpreted histologically as myxoid liposarcoma or myxoid malignant fibrous histiocytoma. We describe FDG PET/CT and MRI findings of a dendritic fibromyxolipoma incidentally detected in a case with rectal adenocarcinoma. The dendritic fibromyxolipoma showed inhomogeneous FDG uptake with SUVmax of 4.0 mimicking malignancy.

What Are the Results of Resection of Localized Dedifferentiated Liposarcomas in the Extremities?

BACKGROUND

Dedifferentiated liposarcoma (DDLPS) is a rare malignancy that transitions from an atypical lipomatous tumor to a sarcoma with a variable morphologic appearance. The behavior of this tumor in the retroperitoneum is aggressive, but the behavior of DDLPS in the extremities is less well-defined because it is rare. Few reports have assessed the imaging features and clinical outcomes of primary DDLPS in the extremities.

QUESTIONS/PURPOSES

In patients with primary DDLPS of the extremity, we asked the following questions: (1) How frequently do additional primary malignancies occur in patients with DDLPS? (2) What is the rate of overall survival, metastases, and local recurrence in DDLPS? (3) What factors are associated with metastasis-free survival and local recurrence in DDLPS?

METHODS

We defined DDLPS as a biphasic neoplasm that transitions from an atypical lipomatous tumor (ALT) to a sarcoma of variable morphologic appearance and histologic grades. We retrospectively evaluated the medical records of patients with DDLPS of the extremities who underwent surgery in our institution between 2003 and 2017. During that time, 16 patients were treated for this diagnosis; one was excluded from this study because the patient did not have an MRI, leaving 15 patients (nine men, six women; their median [range] age was 67 years [42 to 87]) for evaluation. All had a minimum of 2 years follow-up (median [range] 54 months [25 to 136]); 14 of 15 have been seen in the last 5 years (one patient, who was doing well at the time, was lost after 9 years of follow-up). In 11 patients, MRI demonstrated two components: an ALT component with high intensity on both T1-weighed and T2-weighted sequences and a dedifferentiated component low-to-intermediate intensity on T1-weighed and heterogeneous hyperintensity on T2-weighted sequence. Nine patients were evaluated using 2-deoxy-2-18F-fluoro-D-glucose positron emission tomography (FDG-PET) combined with CT (PET/CT). PET/CT showed a biphasic pattern with a close relationship to MRI findings. The dedifferentiated component presented with high FDG uptake (median [range] maximum standardized uptake value 5.1 [1.9 to 22.6]), while the atypical lipomatous tumor component showed almost no FDG uptake. In all patients, immunohistochemical studies of p16 and cyclin-dependent kinase-4 (CDK4) were investigated. Positive staining for both p16 and CDK4 were seen in 13 of 15 patients.We retrospectively evaluated the electronic medical records of all patients in our institution for the presence of additional primary malignancies, local recurrence-free survival, metastasis-free survival, and overall survival. The survival rate was estimated using the Kaplan-Meier method. The Wilcoxon exact test was used to determine the prognostic importance of the following survival variables: age, sex, maximum tumor size, radiotherapy, and surgical margin.

RESULTS

Seven additional primary malignancies developed in five of 15 patients (two lung cancers, two sarcomas, one renal cell cancer, one uterine cancer, and one non-Hodgkin lymphoma). The 3- and 5-year metastasis-free survival rates were 86% (95% CI 0.67 to 1.00) and 75% (95% CI 0.49 to 1.00), respectively. With the numbers available, we found no factors associated with metastasis-free survival. The 3- and 5-year overall survival rates were 100% (95% CI 1.00 to 1.00) and 88% (95% CI 0.65 to 1.00), respectively. Three of 15 patients had local recurrence. The 3- and 5-year local recurrence-free survival rates were 86% (95% CI 0.67 to 1.00) and 75% (95% CI 0.49 to 1.00), respectively. Large (> 15 cm) tumors were more likely to have a local recurrence (p = 0.04).

CONCLUSIONS

In this small series, we found that the extremities are a favorable site for DDLPS compared with the retroperitoneum, although we did not directly compare the two sites. This rare tumor has a relatively high likelihood of being associated with other malignancies. We believe patients should be assessed and monitored carefully for this possibility. In the future, larger studies are needed to better define predictors of local recurrence, although the tumor's size may be associated with a greater propensity for local recurrence.

LEVEL OF EVIDENCE

Level II, prognostic study.

Retroperitoneal tumors: Review of diagnosis and management

Retroperitoneal tumors are extremely rare tumors occurring in the retroperitoneum. Retroperitoneal tumors are divided into benign tumors and malignant tumors, including retroperitoneal sarcoma. Approximately 70-80% of primary retroperitoneal soft-tissue tumors are malignant; however, these only account for 0.1-0.2% of all malignancies. Retroperitoneal sarcoma is an orphan malignant disease with a low incidence. The information on benign retroperitoneal tumors is limited. The American Joint Committee on Cancer/TNM classification updated to the 8th edition in 2017. In 2010, three new drugs for soft tissue sarcoma were approved based on the results of phase III trials, but the histological subtypes of the patients enrolled in the trials of each drug differed. Recently, in addition to surgery for retroperitoneal sarcoma, the effectiveness of perioperative radiation therapy has become interesting. For malignant retroperitoneal tumors and retroperitoneal sarcoma, survival improvement and locoregional recurrence prevention can be undertaken by carrying out surgery to secure negative margins with wide and combined resection of some adjacent organs, and cooperation with a trained medical team comprising of radiologists, pathologists and medical oncologists in centralized hospitals. Some clinical trials aimed at further improving treatment results by adding preoperative chemotherapy and radiation therapy based on histological confirmation using a correct needle biopsy are in progress. In recent years, molecular profiling has been used to select eligible patients for chemotherapy. In the future, precision medicine with next-generation sequencing technology will be expected among the diverse and potential future treatments for retroperitoneal sarcoma. In this review, we summarized the current state of retroperitoneal tumors and retroperitoneal sarcoma.

A Rare Case of Vulvar Hibernoma Treated With Resection

Hibernoma is a rare benign neoplasm of brown adipose tissue most frequently involving the thigh, shoulder, back, and neck. Differentiating this benign entity from other lipomatous tumors such as well-differentiated liposarcoma is essential, given the different surgical approaches and prognosis associated with each diagnosis. It is helpful for the radiologist to recognize the uncommon locations of hibernoma, as well as characteristic imaging features, in order to properly include it in the differential considerations. Here we present a rare case of symptomatic vulvar hibernoma in a 25-year-old woman treated with surgical excision. 

Untreated plasmacytoma of bone containing macroscopic intralesional fat and mimicking intraosseous lipoma: A case report and review of the literature

Solitary plasmacytoma is a rare form of plasma cell neoplasm defined by local neoplastic accumulation of monoclonal plasma cells in the absence of systemic proliferative plasma cell disease. In this case report, a 65-year-old female with remote past medical history of papillary thyroid cancer presented with shoulder pain and radiographs showing an aggressive osteolytic lesion presumed to represent an osseous metastasis. The subsequent MRI and CT examinations demonstrated diffuse intralesional macroscopic fat without a nonlipogenic soft tissue component or focal, nodular mass-like enhancement. The presence of macroscopic fat in an untreated osseous lesion suggested a benign lesion with the favored diagnosis an intraosseous lipoma with non-displaced pathological fracture. Therefore, the decision was made to forego image-guided percutaneous biopsy and instead proceed directly to open surgical biopsy and partial distal claviculectomy. Pathology of the resected specimen showed focally dense infiltration of plasma cells within the marrow space and scant hematopoiesis compatible with a plasma cell neoplasm. To the best of our knowledge, this is first case report of solitary plasmacytoma of bone, or any untreated plasma cell neoplasm, containing macroscopic fat upon imaging. The decision to forego image-guided percutaneous biopsy had significant treatment implications as the primary therapy for patients with SPB is not surgical, but localized radiation therapy. Based on this case, solitary plasmacytoma of bone may be included as one of the rare fat containing malignant bone lesions and imaging guided percutaneous biopsy should be considered in symptomatic fat-containing bone lesions.

Oral liposarcoma in elderly: Case report and literature analysis

RATIONALE

Oral liposarcoma is an extremely rare lesion that is often clinically misdiagnosed as a benign lesion because of its asymptomatic and indolent clinical course. we report a case of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) of buccal mucosa, provisionally diagnosed as lipoma.

PATIENT CONCERNS

A 97-year-old female was referred to dentistry and oral surgery department with an asymptomatic mass on the right buccal mucosa which had been present for an unknown period of time.

DIAGNOSIS

Magnetic resonance imaging demonstrated a well-circumscribed lesion at the right buccal mucosa, and a lipoma was suspected.

INTERVENTIONS

Surgical removal was performed, and a diagnosis of ALT/WDL was made. She and her family refused additional treatment due to her age.

OUTCOMES

At the 10 months follow-up, the patient remained free of disease.

LESSONS

The indolent clinical course and small size of oral liposarcoma can lead to provisional clinical diagnosis of benign lesion.

Meta-Analysis of the Diagnostic Accuracy of Primary Bone and Soft Tissue Sarcomas by 18F-FDG-PET

OBJECTIVES

The goal of this meta-analysis was to assess the use of FDG-PET in the diagnosis of primary bone and soft tissue sarcomas.

SUBJECTS AND METHODS

Several databases, including PubMed, Embase, Cochrane Library, and Web of Science, were searched. In addition to sensitivity and specificity, the diagnostic accuracy region for detecting and grading sarcomas were pooled using bivariate and hierarchical summary receiver-operating characteristic (HSROC) models. Subgroup analysis included pooling soft tissue and bone sarcomas separately, and sensitivity analysis included high-quality studies. The quality of eligible studies was assessed using QUADAS-2.

RESULTS

Of the 1,258 papers screened, 21 studies satisfied the inclusion criteria. The pooled sensitivity and specificity of FDG-PET combined with CT for the detection of sarcomas were 89.2 and 76.3%, respectively. These diagnostic accuracy measures were higher when combined with CT than those of PDG-PET alone. Diagnostic accuracy for bone and soft tissue lesions were comparable but slightly better for soft tissue tumors. Pooling only the high-quality studies with low risk of bias yielded a sensitivity of 88.5% and specificity reduced to 65.6%. There was no evidence for publication bias, but significant heterogeneity among the studies was apparent. This study also showed that FDG-PET can efficiently differentiate between benign and malignant tumors, with a mean standard uptake value of maximally 2.52 units in benign and 6.81 units in malignant tumors (89.2% sensitivity and 75.1% specificity).

CONCLUSION

Our findings indicate FDG-PET can efficiently differentiate between benign and malignant bone and soft tissue tumors. We also found that FDG-PET improves accuracy in diagnosing soft tissue sarcomas when combined with CT.

Multiple gastric angiolipomas: A case report

BACKGROUND

Angiolipoma is a benign tumor and is generally found in subcutaneous tissues. Angiolipomas are rare in the gastrointestinal tract, including the stomach. Preoperative diagnosis of the tumor is difficult, although there are several radiological examinations such as computed tomography and endoscopic ultrasound.

CASE SUMMARY

We report a 24-year-old Chinese man with multiple gastric angiolipomas, with a positive stool occult blood examination. Endoscopic biopsy only showed nonspecific inflammation. Histological examination of the specimen by endoscopic snare resection showed that the tumor consisted of adipose tissues and blood vessels. We also performed a literature review. After the use of proton pump inhibitor, the fecal occult blood test was negative. Due to the difficulty of resecting multiple lesions in the stomach completely and the benign characteristics of angiolipoma, we chose to have regular upper gastrointestinal endoscopy evaluation of the lesion. No evidence of significant change in lesion size was detected after 3-years follow-up.

CONCLUSION

Gastric angiolipoma is rare, and benign neoplasm should be considered when lesions occur submucosally in the gastrointestinal tract.

PET in the Diagnostic Management of Soft Tissue Sarcomas of Musculoskeletal Origin

Soft tissue sarcomas (STSs) account for less than 1% of adult solid tumors and about 7% of pediatric malignancies, causing 2% of cancer-related deaths. With the advent of PET-computed tomography (CT), the value of (18) fluorine-2-fluoro-2-deoxy-d-glucose (FDG) PET imaging to improve the management of STSs has been explored. FDG PET imaging has been found useful in restaging and treatment response assessment. This article reviews current knowledge and application of FDG PET-CT in initial diagnosis, staging, restaging, treatment response monitoring, and prognosis, with a brief overview of the most common histologic subtypes of STS.

18F-FDG PET/CT and MRI features of myxoid liposarcomas and intramuscular myxomas

OBJECTIVE

To examine the imaging characteristics of intramuscular myxomas (IM) and myxoid liposarcomas (MLS) on ¹⁸F-FDG PET/CT and MRI.

MATERIALS AND METHODS

With IRB approval, our institutional imaging database was searched for pathologically proven IM and MLS evaluated by ¹⁸F-FDG PET/CT and MRI. PET/CT and MRI imaging characteristics were recorded and correlated with pathologic diagnosis.

RESULTS

We found eight patients (2 M, 6 F) with IM (mean age 65.6 ± 10.4 years) and 16 patients (7 F, 9 M) with MLS (mean age 42.8 ± 16.3 years). MRI was available in 7/8 IM and 15/16 MLS patients. There was no significant difference between the two groups in SUVmax (IM 2.7 ± 0.8, MLS 3.0 ± 1.0; p = 0.35), SUVmean (1.7 ± 0.4, 1.5 ± 0.5; p = 0.40), total lesion glycolysis (101.8 ± 127.3, 2420.2 ± 4003.3 cm³*g/ml; p = 0.12), metabolic tumor volume (62.3 ± 71.1, 1742.9 ± 3308.0 cm³; p = 0.17) or CT attenuation (p = 0.70). MLS occurred in younger patients (p = 0.0015), were larger (16.4 ± 8.2 vs. 5.6 ± 2.5 cm; p = 0.0015), more often T1 hyperintense (p = 0.03), with nodular enhancement (p = 0.006), and macroscopic fat on CT (p = 0.0013) and MRI (p = < 0.001) compared to myxomas.

CONCLUSIONS

IM and MLS most commonly demonstrate low-grade FDG activity and overlapping metabolic measures on PET/CT. MRI is useful in differentiation, but MLS can present without macroscopic fat on MRI, underscoring the importance of radiologic-pathologic correlation for accurate diagnosis.

Hibernoma as an incidental finding in the 18F-FDG PET/CT of a patient with melanoma

Despite being benign tumors, hibernomas show intense fluorine-18-fluorodeoxyglucose uptake, as they are derived from brown fat, which is frequently seen as hypermetabolic fatty areas on PET/CT. We present the case of a patient with cutaneous melanoma, diagnosed with a cervical hibernoma mimicking a metastatic lymph node at fluorine-18-fluorodeoxyglucose PET/CT. Being aware of the metabolic behavior and radiologic appearance of this entity may prevent reporting false-positive lesions, especially in an oncologic setting.

A Rare Case of Hibernoma Occasionally Identified by 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in a Patient with Lung Cancer

Hibernoma is a benign tumor arising from brown fat tissue. Conventional imaging techniques are not able to differentiate it from other benign lesions or malignant fatty tumors. We report the case of a 73-year-old patient who underwent a thorax computed tomography (CT) and was then referred to our department for metabolic assessment of a solitary lung nodule. An F18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) scan was performed and demonstrated, in addition, a highly metabolic fat-containing lesion mimicking a malignant fatty tumor in the left great pectoralis muscle. The lesion was excised and resulted to be a hibernoma. This case shows that hibernoma can appear as a malignant-like lesion on 18F-FDG-PET/CT scan as per other imaging techniques, and the grade of FDG uptake does not accurately reflect malignancy in this fat-containing tumor. However, 18F-FDG-PET/CT with its whole-body scanning capability may represent a useful imaging tool in identifying, in the course of an imaging study for oncological evaluation, additional incidental findings such as benign fat-containing lesions that may require a surgical approach.

Fat-Containing Hypermetabolic Masses on FDG PET/CT: A Spectrum of Benign and Malignant Conditions

OBJECTIVE

This article focuses on identifying the imaging appearances of hypermetabolic fatty masses and masslike lesions on PET/CT and understanding the diagnostic challenges radiologists may face while interpreting findings of these lesions on PET/CT. This article provides an approach to aid in the diagnosis of these lesions and the appropriate management of patients.

CONCLUSION

Both malignant and benign fat-containing masses and masslike lesions can show hypermetabolic activity on PET/CT. Although the differential diagnosis is broad, clinical history, anatomic location, and knowledge of anatomic variants and imaging features can help radiologists avoid misinterpretation of benign fatty lesions as malignancy.

Soft-Tissue Sarcomas: An Update for Radiologists Based on the Revised 2013 World Health Organization Classification

OBJECTIVE

Soft-tissue sarcomas are a diverse group of malignancies, and our rapidly improving understanding of their molecular pathogenesis and treatment is leading to better clinical outcomes. The revised 2013 World Health Organization (WHO) classification of soft-tissue sarcomas introduced several important changes. We provide a comprehensive overview of the relevant changes for radiologists.

CONCLUSION

Rapid advances in the understanding of the pathogenesis and molecular biology of soft-tissue sarcomas led to major revisions in the 2013 WHO classification. To provide optimal multidisciplinary patient care, radiologists must remain up-to-date with the latest developments in the field of soft-tissue sarcomas to best correlate the histologic and imaging features of the various types of tumors and understand the unique patterns of treatment response and disease recurrence.

Assessing the role of ¹⁸F-FDG PET and ¹⁸F-FDG PET/CT in the diagnosis of soft tissue musculoskeletal malignancies: a systematic review and meta-analysis

PURPOSE

Twelve years ago a meta-analysis evaluated the diagnostic performance of (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in assessing musculoskeletal soft tissue lesions (MsSTL). Currently, PET/CT has substituted PET imaging; however, there has not been any published meta-analysis on the use of PET/CT or a comparison of PET/CT with PET in the diagnosis of MsSTL. Therefore, we conducted a meta-analysis to identify the current diagnostic performance of (18)F-FDG PET/CT and determine if there is added value when compared to PET.

METHODS

A systematic review of English articles was conducted, and MEDLINE PubMed, the Cochrane Library, and Embase were searched from 1996 to March 2015. Studies exploring the diagnostic accuracy of (18)F-FDG PET/CT (or dedicated PET) compared to histopathology in patients with MsSTL undergoing investigation for malignancy were included.

RESULTS

Our meta-analysis included 14 articles composed of 755 patients with 757 soft tissue lesions. There were 451 (60 %) malignant tumors and 306 benign lesions. The (18)F-FDG PET/CT (and dedicated PET) mean sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for diagnosing MsSTL were 0.96 (0.90, 1.00), 0.77 (0.67, 0.86), 0.88 (0.85, 0.91), 0.86 (0.78, 0.94), and 0.91 (0.83, 0.99), respectively. The posterior mean (95 % highest posterior density interval) for the AUC was 0.92 (0.88, 0.96). PET/CT had higher specificity, accuracy, and positive predictive value when compared to a dedicated PET (0.85, 0.89, and 0.91 vs 0.71, 0.85, and 0.82, respectively).

CONCLUSION

(18)F-FDG PET/CT and dedicated PET are both highly accurate in the diagnosis of MsSTL. PET/CT is more accurate and specific and has a higher positive predictive value than PET.

Posterior mediastinal ganglioneuroma with peripheral replacement by white and brown adipocytes resulting in diagnostic fallacy from a false-positive 18F-2-fluoro-2-deoxyglucose-positron emission tomography finding: a case report

Introduction

Ganglioneuroma is a rare tumor in the posterior mediastinum; fat-containing ganglioneuromas are rarely reported. The present case report documents a brown fat-containing, posterior mediastinal ganglioneuroma, which has not been reported previously. Radiological examination, in particular 18F-2-fluoro-2-deoxyglucose-positron emission tomography, suggested that the tumor had low-grade malignant potential. This led to uncertainty at preoperative diagnosis.

Case presentation

An asymptomatic 66-year-old Japanese woman with no significant past medical history was referred for the evaluation of a posterior mediastinal mass. Although its size had not changed in the past 5 years, a malignant lipomatous tumor could not be excluded due to the presence of intratumoral fat and increased 18F-2-fluoro-2-deoxyglucose uptake observed by positron emission tomography imaging. A computed tomography-guided core-needle biopsy revealed a mixture of mature adipocytes, spindle-shaped cells, and fibrotic stroma. Definite diagnosis was not possible, and surgical resection was performed. Three years after the surgery, she remains disease-free.

Conclusions

Histological diagnosis of the surgically resected mass confirmed ganglioneuroma with substantial amounts of white and brown adipose tissues in peripheral areas. The existence of both ganglion cells and brown fat tissue intensified the accumulation of 18F-2-fluoro-2-deoxyglucose, resulting in a false-positive result by positron emission tomography. Considering this, ganglioneuroma should not be excluded either clinically or pathologically in fat-containing, posterior mediastinal tumors.

Correlations between F-18 FDG PET/CT and pathological findings in soft tissue lesions

OBJECTIVE

To evaluate the correlations between F-18 FDG uptake imaged with PET/CT and pathological findings in soft tissue lesions.

METHODS

Fifty-four soft tissue lesions in 47 patients were evaluated. The correlations between the degree of FDG uptake, pathological type and grade, and MRI signal intensity and/or enhancement pattern were evaluated. Tumor FDG uptake was quantified by the maximum standardized uptake value (SUVmax).

RESULTS

Thirty-one lesions were malignant and twenty-three lesions were benign. The difference between SUVmax in the malignant and benign groups was statistically significant (p<0.001). Malignant myxoid lesions and well differentiated liposarcoma showed low FDG uptake. Benign neurogenic lesions showed low FDG uptake while malignant neurogenic tumors showed high FDG uptake, and the difference between SUVmax in the benign and malignant lesions was statistically significant (p<0.001). In a neurofibromatosis type-1 patient who had multiple neurogenic tumors, FDG-PET/CT could distinguish malignant peripheral nerve sheath tumors from other benign lesions with similar MRI findings.

CONCLUSIONS

FDG-PET/CT is useful for differentiating malignant from benign soft tissue lesions, but malignant soft tissue lesions may show various patterns on FDG-PET, and MRI may be helpful for a differential diagnosis.

FDG PET/CT findings in rare sarcomas

The role of FDG PET/CT in management of soft tissue and bone sarcomas has been described in many studies up-to-date. However, contribution of PET/CT to diagnosis and treatment in some types of sarcomas that are seen with low incidence has not been identified properly yet. Clear cell sarcoma, synovial sarcoma of chest and myxoid lyposarcoma are rare types of sarcomas. We aimed to describe the FDG uptake patterns of these rare tumors and find out the role of FDG PET/CT in management of disease.

FDG PET/CT and MR imaging of intramuscular myxoma in the gluteus maximus

Intramuscular myxoma is a rare benign soft tissue tumor which may be mistaken for other benign and low-grade malignant myxoid neoplasms. We present the case of a 63-year-old woman with an asymptomatic intramuscular myxoma discovered incidentally on a whole-body F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography. PET images showed a mild FDG uptake (maximum standardized uptake value, 1.78) in the left gluteus maximus. Subsequent magnetic resonance (MR) imaging revealed a well-defined ovoid mass with homogenous low signal intensity on T1-weighted sequences and markedly high signal intensity on T2-weighted sequences. Contrast-enhanced MR images showed heterogeneous enhancement throughout the mass. The diagnosis of intramuscular myxoma was confirmed on histopathology after surgical excision of the tumor. The patient had no local recurrence at one year follow-up. Our case suggests that intramuscular myxoma should be considered in the differential diagnosis of an oval-shaped intramuscular soft tissue mass with a mild FDG uptake.

Hibernoma: Intense Uptake on F18-FDG PET/CT

Hibernoma is a rare benign but metabolically active tumor of brown fat origin, that can have cross-sectional imaging characteristics similar to those of other fat-containing tumors, such as lipomas and liposarcomas, and its presence can lead to false-positive interpretation by exhibiting increased F18-fluorodeoxyglucose (F18-FDG) activity. A 46-year-old woman was diagnosed with dermatofibrosarcoma protuberans underwent F18-FDG positron emission tomography/computed tomography (PET/CT) for detecting recurrence after excision. F18-FDG PET/CT showed incidental intense uptake in the back in addition to increased F18-FDG uptake at the previous lesion site. To our knowledge, this is the first case report of intense F18-FDG uptake in hibernoma in Korea.

Computed tomography scan-driven selection of treatment for retroperitoneal liposarcoma histologic subtypes

BACKGROUND

Well differentiated (WD) and dedifferentiated (DD) retroperitoneal liposarcoma (RPLS) have distinct biologic behaviors. Consequently, the therapeutic approaches for these tumors differ and mandate an accurate preoperative diagnosis. The authors of this report evaluated whether computed tomography (CT) can be used to differentiate between WD and DD RPLS.

METHODS

Imaging studies (CT, magnetic resonance imaging, and positron emission tomography-CT) from 78 patients with RPLS who underwent surgery at the University of Texas M. D. Anderson Cancer Center (UTMDACC) between 2001 and 2007 were reviewed by a senior bone and soft tissue sarcoma radiologist who was blinded to the final histopathologic diagnosis. A focal nodular/water density area within an RPLS was interpreted as a marker suggestive of DD. Correlations between imaging diagnosis, histology, and clinical outcome were analyzed.

RESULTS

The study radiologist identified 60 RPLS as DD and 17 RPLS as WD. A radiologic diagnosis of a WD was correlated with preoperative biopsy and postoperative histology in all patients (100%). Focal nodular/water density was a very sensitive marker of DD (97.8%); however, it had relatively low specificity (51.5%). Sixteen WD RPLS (48.5%) contained focal nodular/water density areas, leading to their misdiagnosis as DD; half of those tumors had hypercellular WD. Of 78 preoperative biopsies, 22 (28.2%) were performed at UTMDACC under CT guidance. Preoperative histologic diagnoses obtained from 12 biopsies derived from focal nodular/water density areas were confirmed as unchanged on final pathology; whereas, in 50% of biopsies that were not taken from a suspicious area, DD histology was misdiagnosed as WD.

CONCLUSIONS

When CT features are suggestive of WD, no further diagnostic tests are needed for tumor characterization. Moreover, CT can accurately identify most DD, thereby rendering their under-treatment unlikely; however, a CT-guided biopsy is needed to differentiate between DD and WD RPLS that contain focal nodular/water density areas, thereby avoiding their over treatment.

Mediastinal hibernoma simulates a malignant lesion on dual time point FDG imaging

Dual time point 2-deoxy-2-[18F] fluoro-d-glucose (FDG) positron emission tomography (PET) imaging has been shown to be useful in helping differentiate benign from malignant lesions. An enhancing mediastinal mass of fat and water density was incidentally detected on computed tomography (CT) in a patient being evaluated for thoracic trauma. He subsequently underwent dual time point FDG PET/CT imaging which revealed a significant rise in standard uptake value (SUV) within the lesion over time, favoring a malignant etiology. Biopsy proved the lesion to represent a hibernoma, an uncommon benign fatty tumor. This case exemplifies the complexity of tissue metabolic properties, and the difficulty in establishing absolute criteria for benign and malignant processes.

Surgical approach to a large dumbbell-shaped pelvic lipoma extending through the obturator foramen

Lipomas are the most commonly occurring mesenchymal tumors. We report a technique used to manage a patient with a large dumbbell-shaped pelvic lipoma passing through the obturator foramen. Using the combined expertise of an orthopedic and pelvic surgeon, successful and safe removal of this benign dumbbell-shaped pelvic lipoma was achieved.

Cervical Hibernoma Demonstrating Uptake on Tc-99m Lymphoscintigraphy

A hibernoma is an uncommon, benign tumor composed of brown adipose tissue. It is a rare but documented cause of neck masses. Hibernomas may be first diagnosed not by clinical examination, but incidentally through radiologic tests assessing the metabolic activity of certain tissues. These tumors are by definition benign entities but, given their propensity for growth over time, they require complete extirpation to prevent recurrence. Different radiologic modalities have been used to evaluate hibernomas, including computed tomography scan, magnetic resonance imaging, fluorine-18 fluoro-2-deoxy-D-glucose positron emission tomography, and angiography. It is rare for a hibernoma to be discovered through Tc-99m lymphoscintigraphy.