Popliteal subcutanous fibrolipoma mimicking atypical lipomatous tumor
Presentation
Painless swelling in the popliteal fossa of the right knee.
Patient Data
A well defined lesion of fat signal is seen within lateral aspect of the popliteal fossa. It's seen located within the deep subcutaneous fat planes being epimuscular abutting the gastrocnemius muscles. The lesion shows predominant fat signal (high T1, T2 signal with signal suppression on fat suppressed techniques) intermingled with areas and bands of low T2 signal and high STIR signal.
Preliminary diagnosis of atypical lipomatous tumor/liposarcoma were considered after the imaging findings.
The mass on CT shows heterogeneous density with predominant fat density intermingled with areas and bands of high density.
Specimen: Two specimens from soft tissue swelling in the popliteal fossa/knee, excision biopsy.
Gross picture:
1) Well defined mass measured 9x 5x 5cm, with soft tissue yellowish greasy section, with rubbery whitish areas, inked resection margin.
2)Flattened soft pinkish tissue piece measured 4 x 4cm.
Microscopic picture: Sections examined from both specimens revealed benign tumor formed of lobules of mature adipocytes separated by fibrovascular sepate of variable thickness with thick collagen bundles. No evidence of atypia or malignancy.
Diagnosis: Fibrolipoma-No malignancy.
Case Discussion
Lipomas are the most common masses in the subcutaneous tissues. Lipomas have different subtypes and fibrolipoma is a subtype consisting of mature fat cells and bands of fibrous connective tissue.
Common locations for fibrolipomas include oral cavity, esophagus and parathyroid glands. Fibrolipoma of the subcutaneous planes are uncommon.
Radiographic features include heterogeneous masses with areas of fat signal (high signal on T1 & T2 WI with signal suppression on fat suppressed techniques), intermingled with bands of low signal showing enhancing areas on post contrast series.
DDx includes lipoma, atypical lipomatous tumor, liposarcoma, spindle cell lipoma, pleomorphic lipoma
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