From the Guidelines
Lipomatous (fatty) tumor refers to a growth or tumor composed primarily of fat cells, with atypical lipomatous tumors (ALTs) being a specific type that has a propensity for local relapse but little capacity for metastatic spread, as noted in the UK guidelines for the management of soft tissue sarcomas 1.
Definition and Characteristics
Lipomatous tumors are typically soft, movable under the skin, and generally harmless. They can occur anywhere in the body where fat is present but are most commonly found just beneath the skin. A common example is a lipoma, which is a benign (non-cancerous) tumor composed of fat tissue.
Diagnosis and Differentiation
The diagnosis of atypical lipomatous tumors can be challenging, and MRI with expert review can differentiate between large, deep lipomas and ALTs in up to 69% of cases, but the defining diagnostic test is the molecular demonstration of amplification of the MDM-2 cell cycle oncogene by fluorescence in-situ hybridisation, which can be done on percutaneous core needle biopsy 1.
Management Strategies
Surgical resection is the usual treatment for ALT, with complete en bloc resection preserving adjacent neurovascular structures but without attempting to gain wide surgical margins, affording long-term local control, as recommended in the UK guidelines 1. In some cases, especially in older patients with significant comorbidities or where surgery is likely to be morbid, radiological surveillance or adjuvant radiotherapy may be considered.
Prognosis and Follow-Up
The prognosis for atypical lipomatous tumors is mostly excellent, with excellent rates of long-term local control following surgical resection. Patients can be discharged to primary care with re-referral only if there is clinical suspicion of recurrence, highlighting the importance of post-operative follow-up and wound care 1.
From the Research
Definition and Characteristics of Lipomatous Tumors
- Lipomatous tumors are common soft tissue tumors, with lipoma being the most frequent type 2.
- These tumors can be benign or malignant and may vary in presentation and management based on their histological subtype 2, 3.
- Lipomatous lesions can arise within soft tissues, bone, neurovascular structures, and synovium, with the majority being benign 4.
Diagnosis and Differentiation
- Diagnosis of lipomatous tumors often requires diagnostic biopsy, but clinical and radiological features can aid in differentiation 5.
- MRI features such as thick septation, presence of a non-adipose mass, foci of high T2/STIR signal, and contrast agent enhancement can indicate malignancy 5.
- 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) can also be used for differential diagnosis, with lipomas showing a significantly lower SUVmax than atypical lipomatous tumors and lipomatous sarcomas 6.
Types of Lipomatous Tumors
- Benign lipomatous tumors include lipomas, elastofibroma dorsi, angiolipoma, lipoblastoma, and hibernoma 4.
- Malignant lipomatous tumors include liposarcomas, such as myxoid liposarcomas and dedifferentiated liposarcomas 6.
- Atypical lipomatous tumors (ALTs) are intermediate in nature and can be challenging to differentiate from lipomas using MRI 6.