Differentials
Liposarcoma
SIGNS / SYMPTOMS
The majority of liposarcomas present at a size >5 cm, while most lipomas are <5 cm in size. Studies suggest that a size of 10 cm or larger is a strong discriminating feature for liposarcoma.[20]
Often feel firmer to palpation than the soft, doughy feel of a lipoma.
Liposarcomas can gain a very large size, either growing slowly over many years or rapidly over a short period of time. Lipomas are generally <5 cm in size and grow slowly or remain static in size.
Retroperitoneal position is suggestive of a liposarcoma because lipomas in this position are exceedingly rare.
INVESTIGATIONS
Imaging with MRI or CT may provide evidence that a lesion is a liposarcoma.
In liposarcomas, septations or nodules generally demonstrate marked enhancement following administration of intravenous gadolinium (whilst lipomas are typically nonenhancing or show only faint enhancement).[20]
Histologic examination of biopsy sample: adipocytes with nuclear atypia to include hyperchromasia, size variation, and nuclear membrane irregularities. Lipoblasts (atypical adipocytes with cytoplasmic vacuoles which indent the nucleus), when present in the appropriate histologic background, are strongly indicative of liposarcoma.
Liposarcomas are histologically subclassified into well-differentiated, dedifferentiated, myxoid, pleomorphic and mixed types, each with a unique morphologic pattern.
Atypical lipomatous tumor or well-differentiated liposarcoma can be confirmed by testing the excised specimen for MDM2 or CPM genes.[30]
Epidermoid cyst
SIGNS / SYMPTOMS
Subcutaneous epidermoid cysts are usually rounded and firm, whereas lipomas have a characteristic soft, doughy texture.
Central punctum often visible, through which a white exudate can be expressed.
INVESTIGATIONS
Definitive diagnosis is made upon excision and histologic examination.
Histologic examination: benign simple cysts lined by stratified squamous epithelium with an intact granular cell layer. Within the cyst lumen, there is characteristic laminated keratin debris. In cysts that have previously ruptured, a foreign-body giant cell reaction is often present.
Abscess
SIGNS / SYMPTOMS
Surrounded by erythema; may develop rapidly over a few days; usually warm and tender to touch.
Patient may be pyrexial.
INVESTIGATIONS
Aspiration usually yields pus.
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