Lipomatous tumors of soft tissue: MR appearance with histological correlation

There is a broad spectrum of lipomatous tumors that involve soft tissues including ordinary lipomas, variants of lipomas, heterotopic lipomas, lipomatosis, hibernomas and liposarcomas. The recognition of these tumors is important to avoid diagnostic pitfalls. The MR imaging appearance of the lesion, including location, shape and internal architecture, suggests the diagnosis of lipomatous tumors. The signal intensity on T1-, T2-, fat-suppressed T2-weighted (FS-T2) images or short tau inversion recovery (STIR), T1- and fat-suppressed T1-weighted images after Gd-DTPA administration can be a useful aid in distinguishing between biologically different types of lipomatous tumors. The imaging features are often characteristic and reflect the histological pattern of the tumors.

We present an overview of the lipomatous tumors and we correlate MR imaging appearance with histological findings.     

Magnetic resonance imaging of lipoma and liposarcoma: potential of short tau inversion recovery as a technique of fat suppression

The present limited retrospective study was performed to assess MR imaging of lipomatous tumours of the musculoskeletal system and to evaluate the potential of the T2 short tau inversion-recovery (STIR) technique for differentiating lipomas from liposarcomas. Magnetic resonance imaging of 12 patients with lipomatous tumours of the musculoskeletal system (eight benign lipomas, three well-differentiated liposarcomas and one myxoid liposarcoma) were reviewed. Benign lipomas were usually superficial and showed homogeneity on T1- and T2-weighted spin echo sequences. Full suppression at T2 STIR was readily demonstrated. In contrast, the liposarcomas in the present series were all deep-seated. Two well-differentiated liposaromas showed homogeneity at long and short relaxation time (TR) but failed to show complete suppression at T2 STIR. One case of well-differentiated liposarcoma (dedifferentiated liposarcoma) and one of myxoid liposarcoma showed mild and moderate heterogeneity at T1 and T2, respectively, and posed no difficulty in being diagnosed correctly. In conclusion, short and long TR in combination with T2 STIR show promise in differentiating benign from malignant lipomatous tumours of the musculoskeletal system, when taken in combination with the position of the tumour.     

MR imaging of liposarcomas: correlation of MR features and histology

The magnetic resonance (MR) imaging features of liposarcoma were correlated with histology in 15 patients. The MR findings for liposarcoma were not specific. The six myxoid liposarcomas and two atypical lipomatous tumors, however, had distinctive MR features, i.e., nodular masses of slightly heterogeneous intermediate to high signal intensity (SI), intermingled with high SI septa on T1-weighted images. The T2-weighted images demonstrated the relative reversal of these regional SI characteristics. Additionally, MR correctly identified the presence of fat in all eight cases in which it was pathologically present. The fat in two atypical lipomatous tumors was inseparable on MR from the subcutaneous fat. Magnetic resonance appears useful for preoperative staging and follow-up studies of liposarcomas. It may be helpful in identifying patients with myxoid liposarcoma and atypical lipomatous tumors who have longer survival times.     

Atypical benign lipomatous tumors in the soft tissue: radiographic and pathologic correlation

This article describes the characteristic imaging findings and correlates them with the pathology in the nonfatty regions of benign atypical lipomatous tumors, which have different findings compared with typical lipomas and well-differentiated liposarcomas. For differentiating these tumors from typical lipomas and well-differentiated liposarcomas, it may be helpful to analyze nonfatty regions in benign atypical lipomatous tumors.     

Differential diagnosis of benign peripheral lipoma from well-differentiated liposarcoma on MR imaging: is comparison of margins and internal characteristics useful?

OBJECTIVE: Our objective was to evaluate the reliability of MR imaging in distinguishing between benign lipoma and well-differentiated liposarcoma. MATERIALS AND METHODS: The MR images of 35 pathologically proven benign lipomas in 35 patients and 23 well-differentiated liposarcomas in 17 patients were retrospectively reviewed. T1-, T2-, and fat-suppressed T1-weighted images were obtained after administration of gadopentetate dimeglumine. Margins and internal characteristics revealed on the MR images and the degree of contrast enhancement of septa were evaluated. These MR imaging findings were compared for well-differentiated liposarcomas and benign lipomas. RESULTS: Completely irregular margins were recognized only in benign lipomas with a pathologic diagnosis of infiltrating lipoma. All tumors without a recognizable nonadipose component were benign lipomas (p < 0.05). As for the well-differentiated liposarcomas, thick septa and nodular or patchy nonadipose components were present more frequently in deep and retroperitoneal lesions than in subcutaneous lesions (p < 0.01). No cases showed only thin septa in the deep lesions of well-differentiated liposarcoma, and all cases showed thick septa or nodular or patchy nonadipose components. The septa in well-differentiated liposarcomas enhanced more strongly than did those in benign lipomas. The septa showed no enhancement relative to muscle in 11 of 19 benign lipomas, whereas the septa showed moderate or marked enhancement in all well-differentiated liposarcomas (p < 0.01). CONCLUSION: Careful assessment of margins and internal characteristics on MR imaging can be a useful aid in further distinguishing between biologically different benign lipoma and well-differentiated liposarcoma.     

Gastric tumors with fatty components. CT findings and differential diagnosis

PURPOSE: To assess the role of CT in diagnosing and characterizing gastric fatty tumors. MATERIAL AND METHODS: We reviewed the CT scans of 16 patients (8 men, 8 women, mean age 52 years) with gastric fatty tumors (11 lipomas, 3 liposarcomas, 1 angiolipoma, 1 teratoma) examined from 1990 to 1999. The differential diagnosis considered primary and secondary lipomatosis, carcinoma engulfing the perivisceral fat and thus mimicking a liposarcoma, mesenchymal gastric and primary peritoneal tumors. RESULTS: Lipomas involved the fundus (7/11), the body (3/11), the antrum (1/11). Multifocality was found in one case. Lesions size ranged 25 to 65 mm (mean 35 mm). All the lipomas showed homogeneous structure with negative (-30 -100) HU values. A pseudocapsule was demonstrated in 7/11 cases. No infiltrative growth was demonstrated. The angiolipoma located in the fundus showed a vascular component with strong contrast enhancement. All the liposarcomas were bigger than 10 cm and there was a strong correlation between pathologic specimen and CT findings. The differentiated liposarcomas showed the classic heterogeneous fatty density; on the contrary the myxoid and the pleomorphic types showed an aspecific structure with necrotic/cystic changes, mostly demonstrated in the myxoid type. The teratoma was a solid mass with fatty, solid, necrotic and calcified components. CONCLUSION: CT allows the diagnosis and characterization of gastric fatty tumors. The preoperative diagnosis of lipomas plays a major clinical role because it often makes surgery unnecessary.     

Computed tomography of lipomatous and myxoid tumors

Thirty-two lipomatous and myxoid tumors were examined by computed tomography (CT). An attempt was made to correlate the radiographic appearance of the tumor to different histologic types of these tumors. It was found that a well delineated lipomatous lesion with uniform radiographic density, an attenuation value below -73 Hounsfield units (HU) and absence of contrast enhancement can be considered strongly suggestive of a benign lipoma. Atypical lipomas, myxoma and well differentiated liposarcomas have good delineation against the surrounding tissue with no peripheral hypervascularity in the majority of cases. The attenuation values varied between -83 and +38 HU. Liposarcomas of myxoid type, mixed myxoid and round-cell type, round-cell type, and pleomorphic type were all poorly delineated with attenuation values between +12 and +38 HU and with varying contrast enhancement. Thus CT can be considered to play an important role in the preoperative evaluation of lipomatous and myxoid tumors of the soft tissues. Besides valuable topographic information CT helps, to some extent, to differentiate between various types of lipomatous tumors.     

Lipomatous tumors of the pelvis in women: spectrum of imaging findings

Pelvic tumors that contain fat are common findings in women. Although the majority of these lipomatous tumors are benign cystic ovarian teratomas, other diseases should be considered in the differential diagnosis: malignant degeneration of a benign cystic ovarian teratoma, nonteratomatous lipomatous ovarian tumors, lipomatous uterine tumors, benign pelvic lipomas, and pelvic liposarcomas. Although these diseases are rare, their differentiation can be clinically significant. While most of these tumors are treated by surgical excision, asymptomatic lipomatous uterine tumors and benign pelvic lipomas may require no therapy. Additionally, correct identification of a malignant lipomatous tumor will affect both prognosis and surgical planning. The purpose of this essay is to illustrate the imaging findings of these conditions.     

CT and MR imaging of fatty tumors of the liver

The presence of fat in hepatic masses narrows the range of differential diagnoses down to hepatic angiomyolipoma, lipoma, adenoma, hepatoma, metastatic fatty tumors of the liver, focal fatty infiltration of the liver, and extrahepatic fatty masses such as intraperitoneal implants from malignant teratomas, and packed omentum. We report six hepatic tumors containing fat (lipoma, hepatocellular carcinoma, and calcified mass with fat-fluid level) with CT and magnetic resonance (MR) imaging. The distribution of fat was diffuse in the lipomas and some hepatocellular carcinomas and localized in other hepatocellular carcinomas and fat-fluid masses. The density ranged from - 100 to 0 HU. High intensity areas on both T1- and T2-weighted MR images corresponded to the hypodense areas on CT.     

110 subfascial lipomatous tumors. MR and CT findings versus histopathological diagnosis and cytogenetic analysis

PURPOSE: To evaluate whether liposarcoma, atypical lipomatous tumors and lipoma can be differentiated radiologically. MATERIAL AND METHODS: We have retrospectively analyzed CT and/or MR images of 110 subfascial lipomatous lesions. The amount of fat within the tumors was visually graded from the images as: none, 1-75%, 75-95% or 95-100%. The structure of non-fatty tumor components was compared. The images were compared to histopathology and in 37 cases to cytogenetic findings. RESULTS: Only 4 of 20 liposarcomas contained fat. All 4 lesions, histopathologically diagnosed as atypical lipomatous tumors, contained fat but less than 75% of tumor volume. All lesions with more fat than 75% of tumor volume were histologically diagnosed as lipomas. However, one-third of the karyotyped lipomas had ring chromosomes which are considered typical for atypical lipomatous tumors. CONCLUSION: When a tumor is composed more or less solely of fat, the diagnosis of a lipoma or atypical lipomatous tumor with a phenotype simulating a lipoma can be assumed. When the fat content is less than 75% of the tumor volume or non-fatty nodules are found, biopsies from different tumor components have to be performed to exclude malignancy. When no fat is found, imaging does not help in differentiating lipoma or liposarcoma from other soft tissue tumors.     

CT and MR imaging characteristics of intravestibular lipoma

BACKGROUND AND PURPOSE: Intracranial lipomas are uncommon congenital malformations that most often are asymptomatic. A rare subset of intracranial lipomas arises within the vestibule of the inner ear, which can cause sensorineural hearing loss. We present the CT and MR imaging characteristics of lipomas within the vestibule of the inner ear and propose a pathogenetic mechanism for this malformation. METHODS: We retrospectively reviewed five cases of vestibular lipoma. T1-weighted axial conventional spin-echo and T2-weighted axial fast spin-echo sequences were performed in all five cases. Four patients underwent T1-weighted fat-saturated imaging, and one underwent CT scanning with Hounsfield units measured. RESULTS: Four female patients ranging in age from 10 to 40 years and one 26-year-old male patient had sensorineural hearing loss. Two patients had progressive high-frequency loss; one, sudden-onset high-frequency loss; and two, congenital high-frequency loss. All had lesions within the vestibule that displayed hyperintensity on T1-weighted images, isointensity to slight hypointensity on T2-weighted fast spin-echo images, hypointensity with fat saturation, and fat attenuation on CT scans. Three of the cases were associated with lipoma of the cerebellopontine angle. In none of these cases were the cerebellopontine angle and labyrinthine lipomas contiguous. CONCLUSION: Intravestibular lipoma is considered when a focal hyperintense lesion is identified within the vestibule of the inner ear on T1-weighted MR images. Lesion hypointensity on fat-saturated T1-weighted MR images verifies its lipomatous nature and separates it from intralabyrinthine hemorrhage or highly proteinaceous fluid.     

Septum-like structures in lipoma and liposarcoma: MR imaging and pathologic correlation

 Objective. To investigate the septum-like structures in predominantly lipomatous tumors, by correlating fat-suppressed MR images with histopathologic findings. Design and patients. The MR findings of three cases of well-differentiated liposarcoma (atypical lipoma), one case of lipoma-like component of dedifferentiated liposarcoma, and nine cases of lipoma were analyzed. T1-, T2-, and fat-suppressed T1-weighted images after Gd-DTPA administration were obtained. Surgical specimens from five patients (four with liposarcoma and one with lipoma) were also scanned with a MR unit, and compared with the pathologic findings. Results and conclusions. Enhancement features of lipoma and liposarcoma were well visualized on fat-suppressed T1-weighted images after Gd-DTPA administration. The septum-like structures of liposarcoma are thick and enhanced considerably, while septa of lipoma are thin and enhanced only slightly. Pathologically, the septum-like structures of liposarcoma contained muscle fibers and the septa of lipoma represented fibrous capsule. Identification of well-enhanced septa in a predominantly lipomatous tumor helps to differentiate malignant tumors from lipomas. As the septum-like structures of liposarcoma contain a skeletal muscle component the tumor might need more extensive surgical procedures including resection of adjacent muscles.     

Atypical appearance of lipomatous tumors on MR images: high signal intensity with fat-suppression STIR sequences.

Lipomatous tumors generally have signal characteristics that allow them to be diagnosed with great accuracy by means of magnetic resonance imaging. These tumors usually have signal intensities similar to those of subcutaneous fat on both T1- and T2-weighted spin-echo images. Previous reports have not, to the authors' knowledge, described the appearance of lipomatous tumors on images obtained with a short-inversion-time inversion-recovery (STIR) sequence, which can be used to suppress signal from fat. Three lipomatous tumors (two liposarcomas and one lipoma) with signal characteristics unlike those of normal subcutaneous fat at all pulse sequences are presented.     

MR of intracranial epidermoid tumors: correlation of in vivo imaging with in vitro 13C spectroscopy

We analyzed the MR findings of five patients with benign intracranial epithelial tumors, commonly called epidermoids. The neoplasms were categorized into two groups on the basis of T1-weighted MR signal intensity (relative to brain): high-signal-intensity masses (short T1) and low-signal-intensity masses (long T1). Surgical specimens were obtained and analyzed by means of 13C MR spectroscopy. Epidermoids with short T1 values (white epidermoids) had a high lipid content comprising mixed triglycerides containing unsaturated fatty acid residues. Epidermoids with long T1 values (black epidermoids) exhibited a much reduced lipid content with no triglycerides or fatty acids. There was evidence of trace amounts of cholesterol in the black epidermoids. Our data indicate that epidermoids are a heterogeneous group of neoplasms that behave differently with T1-weighted MR imaging and 13C MR spectroscopy. The combination of MR imaging and spectroscopy holds the potential of further elucidating the nature of epidermoids as well as of other forms of neoplasms.     

Foci of signal intensities different from fat in well-differentiated liposarcoma and lipoma: correlation between MR and histological findings

To investigate the histological features of foci, which showed signal intensities different from fat by magnetic resonance (MR) imagings in well-differentiated lipoma-like liposarcomas and a case of lipoma, a retrospective review of these lipomatous tumors was performed to correlate MR and histological findings. Microscopic findings revealed that these foci were also composed of lipomatous tissue. Well-differentiated liposarcoma and benign lipoma associated with such foci should be differentiated from dedifferentiated liposarcoma based on the histological findings.     

Primary liver tumors: diagnosis by MR imaging

MR features of 153 proved primary liver tumors (95 malignant, 58 benign) in 55 patients with hepatocellular carcinoma (21), cholangiocarcinoma (seven), carcinosarcoma (one), hepatoblastoma (one), hemangioma (16), hepatic adenoma (four), focal nodular hyperplasia (three), leiomyoma (one), and hemangioendothelioma (one) were studied retrospectively to determine which techniques are most reliable for lesion detection and which criteria are most useful for differential diagnosis. MR data were correlated with histologic features such as fatty degeneration, fibrosis, and peritumoral edema. Unlike metastatic cancer, hepatocellular carcinoma was best detected (p less than .01) with T2-weighted pulse sequences. The mean tumor-liver T2 difference was 34.4%, while the mean T1 difference was only 21.8%. A tissue-specific diagnosis of hepatocellular carcinoma was possible in 14 of 21 patients by identification of fatty degeneration of the tumor (eight of 17), tumor capsule (five of 21), and/or vascular invasion (six of 21). MR features of peritumoral edema, present in six of 21 patients with hepatocellular carcinoma and in seven of 25 patients with metastases, were exclusively associated with malignant tumors. The large variation in tissue characteristics (relaxation times and proton density) seen in primary liver tumors necessitates the use of multiple pulse sequences to maximize lesion detection. However, the combined use of T1- and T2-weighted spin-echo and T2-weighted phase-contrast images had the advantage of distinguishing benign from malignant primary liver tumors in 48 of 55 patients in this series.     

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

OBJECTIVE: The relative utility of various preoperative diagnostic imaging modalities, including PET (utilizing FDG and FMT), CT, and MR imaging, for evaluation of lipoma and liposarcoma, especially well-differentiated liposarcoma, was investigated. METHODS: Imaging findings in 32 patients with histopathologically documented lipoma, including one with fibrolipoma and one with angiolipoma, and 25 patients with liposarcomas whose subtypes included 10 well-differentiated, 10 myxoid, and 5 other types were reviewed retrospectively. Pre-operative imaging included FDG-PET (n = 44), FMT-PET (n = 21), CT (n = 25), and MR imaging (n = 53). RESULTS: Statistically significant imaging features of MR images favoring a diagnosis of liposarcoma involved lesions containing less than 75% fat (p < 0.001) as well as the presence of septa (p < 0.001). As compared with well-differentiated liposarcoma, benign lesions were differentiated significantly only by the presence of septa (p < 0.001), which also provided significant differentiation on CT (p < 0.05). The mean SUVs for malignant tumors were significantly higher than those for benign lesions in both FDG- and FMT-PET analyses (p < 0.0001, p = 0.0011, respectively). By using a cut-off value for FDG- and FMT-PET set at 0.81 and 1.0 respectively, which provided the highest accuracy, benign lesions were differentiated significantly from liposarcomas (p < 0.001, and p < 0.02). Furthermore, benign tumors and the three subtypes of liposarcoma were divided significantly into four biological grades by FDG- and FMT-accumulation rates (rho = 0.793, p < 0.0001; and rho = 0.745, p = 0.0009, respectively). A cut-off value of 0.81 for FDG-PET provided significant differentiation between benign lesions and well-differentiated liposarcoma (p < 0.01). CONCLUSIONS: The presence of septa on MR images differentiated lipomas from liposarcoma, even well-differentiated type. PET analysis, especially FDG-PET, quantitatively provided not only the differentiation but also the metabolic separation among subtypes of liposarcoma. Interpretation of the visual diagnostic modalities requires extensive experience and carries a risk of ignoring a critical portion of malignancy. PET metabolic imaging may be an objective and useful modality for evaluating adipose tissue tumors preoperatively.     

MR imaging of primary bone and soft tissue tumors

MR imaging of 131 cases with pathologically confirmed primary bone and soft tissue tumors were studied. They included 44 bone tumors (25 benign tumors, 19 malignant tumors) and 87 soft tissue tumors (55 benign tumors, 32 malignant tumors). MR imaging was performed on 0.5T, superconductive magnet system. All tumors were evaluated with T1-weighted, T2-weighted and STIR images. In some cases, contrast enhanced MR imaging with Gd-DTPA was applied. MR imaging was proving to be a valuable technique in the evaluation of patients with primary bone and soft tissue tumors. MR imaging was superior to the other modalities in delineating the extent of the tumor and their relation to surrounding structures in all cases. However, plain radiography and CT were more useful for evaluation of calcification, ossification, cortical destruction and endosteal/periosteal reaction than MR imaging. Direct sagittal and coronal images from MR imaging added accurate assessment for the relation between the tumor and their adjacent structures. MR imaging was of limited value in distinguishing benign from malignant tumors with the demonstration of tumor structures only, especially soft tissue tumors. But in bone and soft tissue tumors which have specific morphologic features and intensity patterns, MR imaging was very useful for diagnosis.     

Imaging of fatty tumors: distinction of lipoma and well-differentiated liposarcoma

PURPOSE: To review the reliability of computed tomographic (CT) and magnetic resonance (MR) imaging features in distinguishing lipoma and well-differentiated liposarcoma. MATERIALS AND METHODS: CT (n= 29) and MR (n = 40) images and radiographs (n = 28) of 60 patients with histologically verified fatty tumors (35 lipomas and 25 well-differentiated liposarcomas) were retrospectively reviewed in 31 females and 29 males (mean age, 56 years; age range, 1-88 years). Images were assessed for adipose tissue content, and non-fatty component was classified (thin and/or thick septa and nodular and/or globular components) as absent, mild, moderate, or pronounced. Also assessed were signal intensity and tissue attenuation of the fatty components and non-adipose elements. RESULTS: Statistically significant imaging features favoring a diagnosis of liposarcoma included lesion larger than 10 cm (P <.001), presence of thick septa (P =.001), presence of globular and/or nodular non-adipose areas (P =.003) or masses (P =.001), and lesion less than 75% fat (P <.001). The most statistically significant radiologic predictors of malignancy were male sex, presence of thick septa, and associated non-adipose masses, which increased the likelihood of malignancy by 13-, nine-, and 32-fold, respectively. Both lipoma and liposarcoma demonstrated thin septa and regions of increased signal intensity on fluid-sensitive MR images. CONCLUSION: A significant number of lipomas will have prominent non-adipose areas and will demonstrate an imaging appearance traditionally ascribed to well-differentiated liposarcoma. Features that suggest malignancy include increased patient age, large lesion size, presence of thick septa, presence of nodular and/or globular or non-adipose mass-like areas, and decreased percentage of fat composition.     

Diagnostic challenge of lipomatous uterine tumors in three patients

Lipomatous uterine tumors are uncommon benign neoplasms, with incidence ranging from 0.03% to 0.2%. They can generally be subdivided into two types: pure or mixed lipomas. A third group of malignant neoplasm has been proposed, which is liposarcoma; however, this is very rare. In this article, we report three patients having lipomatous uterine tumors, including one uterine lipoma and two uterine lipoleiomyomas. All our patients are postmenopausal women, which is the typical presenting age group. They did not have any symptoms and the tumors were only found incidentally on imaging. However, in some patients, symptoms may uncommonly occur. If symptoms occur, these are similar to those of leiomyoma. We illustrate the imaging features of the tumors in our patients with ultrasound, computed tomography (CT) scan and magnetic resonance imaging (MRI). The tumor typically appears as a well-defined homogenously hyperechoic lesion on ultrasound. It shows fat density on CT scan and signal intensity of fat on MRI. MRI is the modality of choice because of its multiplanar capability and its ability to demonstrate fat component of the lesion, as illustrated in our cases. We also discuss the importance of differentiating lipomatous uterine tumors from other lesions, especially ovarian teratoma which requires surgical intervention. Despite the rarity and the common asymptomatic nature of the tumors, we believe that this series of three cases demonstrates a review of a rare tumor which provides important knowledge for patient management.