Well-differentiated liposarcoma/atypical lipomatous tumor

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Well-differentiated liposarcomas (WDLPS) or atypical lipomatous tumors (ALT) are locally aggressive adipocytic soft tissue neoplasms and are the most common form of liposarcomas.

Terminology

Atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLPS) are also termed ‘atypical lipomas’, but this term has been discouraged .

Epidemiology

Atypical lipomatous tumors or well-differentiated liposarcomas account for 40-45% of liposarcomas and constitute the largest subgroup of adipocyte malignancies. They occur mostly in adults with a peak incidence in the 30s and 40s. In childhood, they are extremely rare. Inguinal lesions are more common in men otherwise there is no gender predominance however .

Associations

Atypical lipomatous tumors/well-differentiated liposarcomas may be associated with Li-Fraumeni syndrome .

Clinical presentation

The most common presentation is that of a painless mass. Deep-seated atypical lipomatous tumors/well-differentiated liposarcomas are most often found incidentally .

Complications

If left untreated atypical lipomatous tumors/well-differentiated liposarcomas can dedifferentiate into higher-grade malignancies such as dedifferentiated liposarcoma or undifferentiated pleomorphic sarcoma .

Pathology

Atypical lipomatous tumors/well-differentiated liposarcomas are adipocytic neoplasms characterized by a proliferation of pleomorphic mature adipocytes of different patterns featuring atypical hyperchromatic stromal cells. They are intersected by fibrous septa, might have myxoid or fibrous components and areas of fat necrosis .

Location

Atypical lipomatous tumors/well-differentiated liposarcomas commonly involve the deep soft tissues in particular of the proximal extremities and the trunk .

Common locations include the following :

Rarer locations of involvement include the following :

Classification

Atypical lipomatous tumors/well-differentiated liposarcomas include the following subtypes :

  • lipoma-like liposarcoma
  • sclerosing liposarcoma
  • inflammatory liposarcoma
Macroscopic appearance

Macroscopically atypical lipomatous tumors/well-differentiated liposarcomas usually present as well-circumscribed, large lobulated masses of variable consistency and white to yellowish color. They might display foci of necrosis or small punctate hemorrhages .

Microscopic appearance

The microscopic appearance of atypical lipomatous tumors/well-differentiated liposarcomas includes the following features. Larger tumors and especially retroperitoneal tumors commonly show more than one morphologic pattern within the same lesion:

  • presence of atypical hyperchromatic stromal cells
  • variable number of lipoblasts
  • possibly variations in adipocyte size with nuclear atypia (lipoma-like subtype)
  • possibly copious inflammatory infiltrates (inflammatory subtype)
  • possibly bizarre stromal cells within a fibrillary sclerotic, collagenous background (sclerosing subtype)
Immunohistochemistry

Immunohistochemistry stains are usually positive MDM2 and/or CDK4 .

Genetics

The pathogenesis of atypical lipomatous tumors/well-differentiated liposarcomas involves MDM2 and/or CDK4 nuclear gene amplification .

Radiographic features

Imaging features of atypical lipomatous tumors/well-differentiated liposarcomas resemble that of benign lipomas as discussed in the article lipoma vs well-differentiated liposarcoma and include :

  • size > 5 cm
  • thick or nodular septae (>2 mm) with possible enhancement
  • multinodular tumor margins
  • focal nodular patchy non-fatty tissue components
  • more than ¾ of fatty tissue

They might displace other organs or tissue.

Ultrasound

Usually appears as multilobulated well-defined mass sometimes with hyperechoic foci .

CT

CT usually shows a fat tissue density mass with thick or nodular enhancing septae. Calcifications might be rarely found . 

MRI

On MRI atypical lipomatous tumors/well-differentiated liposarcomas will display a mass of fat isointense signal in all sequences. In addition, atypical lipomatous tumors/well-differentiated liposarcomas will show thick septae or nodular non-lipomatous areas with contrast enhancement .

  • T1: hyperintense
  • T2: hyperintense possibly with prominent high signal foci
  • T2FS/PDFS: hypointense
  • T1 C+ (Gd): moderate to marked enhancement of septae

Radiology report

The radiological report should include a description of the following :

  • form, location and size
  • tumor margins
  • thick septae and septal enhancement
  • amount of non-adipose tissue
  • distance from the muscular fascia
  • relationship to local nerves and vessels 

Treatment and prognosis

The management of choice in atypical lipomatous tumors/well-differentiated liposarcomas is resection, which is curative if complete . The tumors are not sensitive to radiotherapy or chemotherapy . Tumor prognosis is therefore mostly dependent on how amenable the location is to surgical excision. The tumor does not cause distant metastasis unless there is dedifferentiation. Therefore tumors of the mediastinum retroperitoneum or spermatic cord have a worse prognosis, due to their location they are more prone to local recurrence .

Differential diagnosis

Conditions or tumors which can mimic the presentation and/or the appearance of atypical lipomatous tumors/well-differentiated liposarcomas include :

See also