Malignant Fibrous Histiocytoma

Case History: 45-year-old patient with three-month history of swelling in left leg.

MRI showed a heterogenous signal mass in the anterolateral compartment. Mass is located in soft tissues with erosion of cortices of tibia and fibula. Signal changes are also seen in the tibial shaft. Encasement of neurovascular bundle is seen.

FNAC showed a soft tissue sarcoma likely to be malignant fibrous histiocyoma.

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Figure 1. A, B, T2W images show heterogenous signal mass in the anterolateral compartment.

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Figure 2. T1WI show an isointense mass in the anterolateral compartment.

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Figure 3. STIR image shows heterogenous hyperintense mass with signal changes in TIBIA.

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Figure 4. GRE image shows a hyperintese mass.

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Figure 5. T2W image shows encasement of neurovascular bundle.

Malignant fibrous histiocytomas (MFH) (which has more recently been classified as pleomorphic undifferentied sarcoma [PUS] and formerly known as fibrosarcoma) is considered the most common type of soft tissue sarcoma. It has an aggressive biological behavior and a poor prognosis.

Demographics and Clinical Presentation
Typically, MFHs occur in adults (age range 32-80; mean 59 years) with a slight male predilection with an M:F ratio of 1.2:1). Presentation is usually with a painless, enlarging, palpable mass. Although MFH can occur almost anywhere in the body, they have a predilection for the retroperitoneum and proximal extremities. They are usually confined to the soft tissues, but occasionally may arise in or from bone (1%-5%). They are the most frequent soft tissue sarcoma to occur as a result of radiotherapy3 and are also seen as a background of Paget disease.

Pathology
MFH are aggressive tumors which account for 25%-40% of all adult soft tissue sarcoma, making them the most common type.1 However, the classification system is becoming more restrictive, with many tumors being reclassified as variants of myogenic sarcomas.3 Macroscopically, these tumors are typically large (5 cm–20 cm) well-circumscribed but unencapsulated with a grey firm heterogeneous cut surface sometimes with areas of necrosis.

Microscopically, they are heterogeneous fibroblastic tumors made up of poorly differentiated fibroblasts, myofibroblasts, histiocyte-like cells with significant cellular pleomorphism, storiform architecture, and also demonstrate bizarre multi-nucleated giant cells.3 They are sometimes difficult to distinguish from other high grade sarcomas. A number of histological subtypes have been described including: ^2-3

• Storiform-pleomorphic: most common 50%-60%
• Myxoid: 25%, myxofibrosarcoma
• Inflammatory: 5%–10%
• Giant cell: 5%–10%
• Angiomatoid

• Relatively nonaggressive
• Metastases uncommon
• Usually occurs in young adults/adolescents

Radiographic Features
Plain Film
Plain X-rays will demonstrate a soft tissue mass and if arising from bone, an aggressive destructive bony lesion. In some cases, curvilinear or punctate regions of calcification may be demonstrated.

CT
The density of MFH is typically similar to adjacent muscle, with heterogeneous lower density areas if hemorrhage, necrosis, or myxoid material is abundant. The soft tissue component enhances. In up to 15%–20% of cases some mineralization is present.

MRI
MRI is the modality of choice for assessing soft tissue sarcomas, as it is best able to locally stage the tumor. These tumors are typically relatively well-circumscribed, located within or adjacent to muscle, and exert a positive mass effect on surrounding structures due to their (usual) large size at presentation.

• T1

• Intermediate (to low) signal intensity, similar to adjacent muscle.
• Heterogeneity if hemorrhage, calcification, necrosis, myxoid material present.
• Prominent enhancement of solid components.

• T2

• Intermediate to high signal intensity.
• Heterogeneity if hemorrhage, calcification, necrosis, myxoid material present

Treatment and Prognosis
Most MFH are of high-grade (3 and 4) and are aggressive in their biological behavior. They frequently metastasize (30%–50% at diagnosis) and locally recur despite aggressive treatment. The overall 5-year survival is between 25%–70%.

Prognostic factors include :
• Tumor size: smaller being better.
• Location

• Superficial is better.
• Distal is better.

• Histological grade

Examples
A tumor located superficially in the subcutaneous tissues of the distal extremity, and measuring less than 5 cm has a 5-year survival of 80%, whereas a proximal large (> 5 cm) deep tumor has a 5-year survival of 55%.

Treatment usually consists of aggressive en bloc resection with a wide margin. Supplementary neoadjuvant chemotherapy and radiotherapy is especially useful in reducing the local recurrence rate.⁵ Limb-sparing surgery is usually possible.

Differential Diagnosis
General imaging differential considerations include:
• Other sarcomas and soft tissue tumors¹

• Synovial sarcoma.
• Aggressive fibromatosis.
• Benign fibrous tumors.

• Soft tissue metastases.
• Myositis ossificans.

References
1. Ahlén J, Enberg U, Larsson C, et al. Malignant fibrous histiocytoma, aggressive fibromatosis and benign fibrous tumors express mRNA for the metalloproteinase inducer EMMPRIN and the metalloproteinases MMP-2 and MT1-MMP. Sarcoma. 2001;5:143-149.
2. Kumar V, Abbas AK, Fausto N, et al. Robbins and Cotran pathologic basis of disease. W B Saunders Co. (2005).
3. Meyers SP. MRI of bone and soft tissue tumors and tumorlike lesions, differential diagnosis and atlas. Thieme Publishing Group. (2008).
4. Manaster BJ, Disler DG, May DA, et al. Musculoskeletal imaging, the requisites. Mosby Inc. (2002). 5. Skinner HB. Current diagnosis & treatment in orthopedics. McGraw-Hill Medical. (2003).