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.     

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.     

Lipomas, lipoma variants, and well-differentiated liposarcomas (atypical lipomas): results of MRI evaluations of 126 consecutive fatty masses

OBJECTIVE: Our objectives were to evaluate the reliability of MRI in distinguishing simple lipomas, lipoma variants, and well-differentiated liposarcomas (atypical lipomas) and to identify various imaging mimics of well-differentiated liposarcoma. MATERIALS AND METHODS: One hundred twenty-six consecutively imaged grossly fatty masses were retrospectively reviewed. MRI examinations, their prospective interpretations, and their corresponding pathology reports were compared to determine the reliability of MRI in distinguishing simple lipomas, lipoma variants, and well-differentiated liposarcomas. RESULTS: The success of MRI in identifying well-differentiated liposarcomas among other fatty masses was as follows: sensitivity, 100%; specificity, 83%; accuracy, 84%; positive predictive value, 38%; and negative predictive value, 100%. MRI was 100% specific in the diagnosis of simple lipoma. Sixty-three percent of lesions considered suspicious for well-differentiated liposarcoma were actually simple lipomas (13%) and benign lipoma variants (50%), including chondroid lipoma (13%), osteolipoma (6%), hibernoma (6%), lipoleiomyoma (6%), angiolipoma (6%), and infarcted lipoma (13%). CONCLUSION: Because of differences in treatment, prognosis, and long-term follow-up, it is important to preoperatively distinguish simple lipomas from well-differentiated liposarcomas. MRI is highly sensitive in the detection of well-differentiated liposarcomas and highly specific in the diagnosis of simple lipomas. However, when an extremity or body wall lesion is considered suspicious for well-differentiated liposarcoma, it is more likely (64%) to represent one of many benign lipoma variants.     

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.     

Granular cell tumor of the subcutis: CT and MRI findings

Three cases of granular cell tumor (GCT) of the subcutis are presented. Computed tomography showed a mass isodense with muscle with an ill-defined margin. Magnetic resonance imaging showed a mass with inhomogeneous low signal intensity on both T1- and T2-weighted images. Another characteristic feature of subcutaneous GCT is its attachment in part to muscle. Histological examination confirmed the diagnosis in all cases. Received: 20 July 1998; Revision requested: 12 October 1998; Revision received: 30 October 1998; Accepted: 16 November 1998     

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.     

Malignant transformation in bone lipomas

This report presents four cases of presumed malignant transformation within intraosseous lipomas, one occurring in a stage I lesion and three in stage III lesions, according to my classification. These lesions demonstrated radiologic and histologic features of benign lipomas together with histologic fields of either malignant fibrous histiocytoma or liposarcoma. In two of the three patients who were followed up, the tumors were fatal despite amputation. Malignant transformation of a lipoma should be suspected when rapid bone destruction is seen in a stage I radiolucent lipoma. Malignant transformation of stage III lipomas could be mistaken for malignant transformation within bone infarcts.     

The value of fat-suppressed T2 or STIR sequences in distinguishing lipoma from well-differentiated liposarcoma

The objective of this study was to evaluate the diagnostic value of fat-suppressed T2-weighted (FS-T2) images or short tau inversion recovery (STIR) imaging in distinguishing lipoma from lipoma-like subtype of well-differentiated liposarcoma. Spin-echo T1-weighted and STIR or fat-suppression T2-weighted sequences were performed in 60 lipomas and 32 lipoma-like well-differentiated liposarcomas, histologically proven, looking for thick septa or nodules in T1-weighted images and linear, nodular, or amorphous hyperintensities on FS-T2/STIR sequences. Fourteen lipomas (23.3%) showed thick septa and/or nodules on T1, whereas on FS-T2 or STIR sequences only seven (11.7%) displayed hyperintense nodules and/or septa. All well-differentiated liposarcomas contained these signs on FS-T2 or STIR sequences. The presence of hyperintense septa or nodules in a predominantly lipomatous tumor on FS-T2/STIR sequences helps to differentiate malignant tumors from lipomas. Employing the presence of hyperintense nodules and/or septa as criteria of malignancy specificity was 76.6% and sensitivity 100%. Overdiagnoses of well-differentiated liposarcoma can occur due to the presence of non-lipomatous areas within lipomas. Electronic Publication     

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.     

Focal lymphoid hyperplasia in a lipoma, mimicking liposarcoma

Lipomas may contain nonadipose tissue, which can confound the correct imaging diagnosis because features of such neoplasms can mimic findings associated with well-differentiated liposarcomas. Intratumoral nonadipose tissue, such as muscle, cartilage, and fibrous tissue, may be present in lipomas; however, lymphoid hyperplasia in a lipoma is extremely rare. This report describes a case involving a heterogeneous lipoma in a 55-year-old woman in whom the heterogeneous portion of the tumor was in fact a reactive lymphoid hyperplasia encased by the lipoma. The imaging features of this lesion as well as pathological findings of this unusual tumor are discussed.     

Computed tomography of a symptomatic infarcted thoracic lipoma

Intrathoracic lipomas are often asymptomatic and incidentally discovered on routine chest radiographs. An infarcted, pedunculated thoracic lipoma causing chest pain is described. The possibility of liposarcoma was suggested by an inhomogeneous computed tomography appearance and an attenuation value that was greater than that of normal subcutaneous fat.     

Interhemispheric lipoma associated with subcutaneous lipoma

We report an extremely rare case of intracranial lipoma that was associated with subcutaneous lipoma situated on the anterior fontanelle. During ultrasonographic examination of the subcutaneous lesion, intracranial lipoma was incidentally diagnosed. Computed tomography revealed corpus callosum agenesis, interhemispheric lipoma extending into the choroid plexus. Magnetic resonance imaging demontrated the subcutaneous lipoma and also the exact extent of the lesion. The pathogenesis of lipomas is discussed and the literature is reviewed. Received 20 May 1997; Revision received 14 July 1997; Accepted 17 July 1997     

Imaging of atypical lipomas of the extremities: Report of three cases

Atypical lipomas are soft tissue neoplasms which differ from simple lipomas in that they consist of mature fat cells interspersed with occasional areas containing a variable admixture of multinucleated cells, collagen bundles, and adipocytes with large, hyperchromic nuclei. Although these histopathologic features resemble those of liposarcoma, atypical lipomas occuring in the extremities differ from liposarcoma because they have no tendency for distant metastases. Three patients with atypical lipomas involving the posterior compartment of the thigh are presented. The lipomas were imaged with computed tomography (CT) and magnetic resonance imaging (MRI), using a 0.15-T whole body imager. Although all lesions appeared largely lipomatous, the three lesions simulated liposarcoma on both CT and MRI. On CT, each lesion demonstrated small areas of confluent soft tissue density; these areas were hyperintense with adipose tissue on strongly T2-weighted MRI. We conclude that atypical lipoma of the extremities may not be distinguishable from liposarcoma on imaging and that biopsy is necessary for differentiation.     

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.     

A well-differentiated liposarcoma co-existent with leiomyoma

BACKGROUND: The coexistence of a well-differentiated liposarcoma (atypical lipomatous tumor) and benign smooth muscle component in a single soft tissue neoplasm is extremely rare. CASE REPORT: Histologic and immunohistochemical characteristics of tumor, which represented the recurrence of a retroperitoneal atypical lipoma in a 50-year-old female patient are presented in this paper. The tumor represented the recurrence of a retroperitoneal atypical lipoma. Lipomatous component consisted of a mixture of lipoma-like and sclerosing variant of well-differentiated liposarcoma. Characteristically, the heterologous smooth muscle differentiation was manifested as a macroscopically visible nodular growth in the form of a leiomyoma within the adipocytic component. It consisted of intersecting fascicles of spindle cells, which lacked mitoses and significant atypia, and were immunopositive for smooth muscle markers. CONCLUSION: This case of well-differentiated liposarcoma with benign smooth muscle is the first reported tumor of retroperitoneal localization. It is also the first one to exhibit the heterologous smooth muscle component as a distinct leiomyoma.     

MRI characteristics of lipoma and atypical lipomatous tumor/well-differentiated liposarcoma: retrospective comparison with histology and MDM2 gene amplification

Purpose

To review the reliability of MR imaging features for the purpose of distinguishing lipoma and atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL).

Materials and methods

A retrospective review of 87 patients with histologically proven lipomatous tumors was performed. All underwent MR imaging, assessing lipomatous content, septation, and nodules. The associations between these features and tumor diagnosis based on morphology and the presence or absence of MDM2 amplification were explored. The age of the patient and the size and location of the lesion were also recorded for statistical analysis.

Results

Of the 87 patients, 54 were classified as lipomas and 33 as ALT/WDL. MR identified ALT/WDL with a sensitivity of 90.9 % (CI 74.5–97.6) and a specificity of 37.0 % (CI 24.6–51.3). The positive and negative predictive values were 46.9 % (CI 34.5–59.7) and 86.9 % (CI 65.3–96.6), respectively. The mean age of patients with ALT/WDL was greater (60 years [range 40–83 years]) than those with lipoma (52 years [range 10–79 years]) (p?=?0.025). The mean size of ALT/WDL (18.7 cm [range 5–36 cm]) was significantly greater than lipoma (13.9 cm [range 3–32 cm]) (p?=?0.003). Features that increased the likelihood of ALT/WDL included: patient age over 60 years, maximal lesion dimension over 10 cm, location in lower limb, and presence of non-fatty areas, by a factor of 2.61–6.25 times.

Conclusions

ALT/WDL and lipoma have overlapping MR imaging characteristics. The most reliable imaging discriminators of ALT/WDL were size of lesion and lipomatous content, but due to the overlap in the MRI appearances of lipoma and ALT/WDL, discrimination should be based on molecular pathology rather than imaging.     

Cervical epidural lipoblastomatosis: changing MR appearance after chemotherapy

Lipoblastomatosis is a locally infiltrative tumor of embryonic fat. We describe the MR appearance of cervical lipoblastomatosis with epidural extension. The initial MR study showed features of a soft-tissue mass; a subsequent MR examination, performed after chemotherapy, depicted the lesion as a typical lipoma of high signal intensity on T1-weighted images and of intermediate signal on T2-weighted sequences.     

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.