Why Septa Are Thickened in Liposarcoma
Pathophysiologic Basis
Thickened septa in liposarcoma occur because these structures contain proliferating tumor cells, fibrovascular tissue, and entrapped skeletal muscle fibers, rather than the simple fibrous tissue seen in benign lipomas. 1, 2
The septum-like structures in liposarcoma are fundamentally different from those in lipomas:
- In liposarcoma, the septa are thick (averaging 2.22 mm) and contain skeletal muscle fibers, fibrovascular proliferation, and atypical lipoblasts 1, 2
- In benign lipomas, the septa are thin (averaging 1.33 mm) and represent only fibrous capsule tissue without cellular proliferation 1, 2
Histologic Composition of Thickened Septa
The thickened septa in liposarcoma contain several key components that explain their appearance:
- Skeletal muscle component: Entrapped muscle fibers within the septations are a characteristic finding that distinguishes liposarcoma from lipoma 2
- Fibrovascular tissue: Enhanced vascular proliferation within the septa accounts for their prominent enhancement on contrast-enhanced imaging 2, 3
- Tumor cell infiltration: Atypical lipoblasts and other malignant cells infiltrate the septal structures, contributing to their thickness 3
Imaging Correlation
On MRI with gadolinium contrast and fat suppression, these pathologic features translate to specific imaging characteristics:
- Liposarcoma septa show considerable enhancement due to their fibrovascular and cellular composition 2, 3
- Lipoma septa show only slight enhancement because they contain minimal vascular tissue 2
- The presence of well-enhanced, thick septa (>2 mm) in a predominantly fatty tumor is a reliable predictor of malignancy 1, 2
Clinical Significance
The identification of thickened, enhancing septa has critical surgical implications because the muscle fiber component within liposarcoma septa necessitates more extensive surgical resection including adjacent muscles to achieve adequate margins. 2
This differs from lipoma excision, where simple marginal excision is sufficient since the thin septa represent only fibrous capsule 2
Subtype Variations
The degree of septal thickening varies by liposarcoma subtype:
- Well-differentiated liposarcoma: Shows enhanced tenuous to moderate septa with solid tissue components 3
- Myxoid liposarcoma: Exhibits enhanced solid tissues and thickened septa on post-contrast imaging, reflecting the myxoid matrix and vascular proliferation 3
- Dedifferentiated liposarcoma: Demonstrates clear demarcation between fatty and non-adipose solid tissue with variable septal enhancement 3