Dedifferentiated spermatic cord liposarcoma

In a 60-year-old man, physical examination revealed a deep-seated palpable nodule of right inguinal region. Laboratory findings were normal.

Inguinal ultrasonography (US) was performed, using a high-frequency probe. This revealed an ovoid, heterogeneous, and well-defined mass within right inguinal canal, apparently aside spermatic cord. Its maximum diameter was 2.5 cm, and there was no Doppler signal.

Magnetic resonance imaging (MRI) with contrast (Gadolinium) confirmed a mass of low-to-intermediate signal intensity adjacent to spermatic cord in T1- and T2-weighted images, showing moderate contrast enhancement.

Surgical resection was subsequently performed, and pathologic examination confirmed a mesenchymal neoplasm.

Dedifferentiated liposarcoma (DDLS) is a rare and highly malignant form of liposarcoma that arises from well-differentiated liposarcoma (WDLS). The aetiology is unknown, but it has been linked to amplification of the 12q chromosomal region and overexpression of various genes, including MDM2, HMGA2, and CDK4. [1,2]

Retroperitoneum is the usual location of DDLS. Fewer than 5% are situated along spermatic cord. [3] These are fast-growing tumours with a capacity for distant metastasis. Typically, they present as painless masses, although symptoms of groin or abdominal discomfort may ensue [4]

In US studies, liposarcomas appear as heterogeneous, multilobulated, and generally well-defined lesions. The presence of hyperechoic foci may be indicative of fat, but this is neither a sensitive nor a specific finding, given its frequent association with other lipomatous neoplasms. Consequently, the diagnostic role of US is limited. [5]

Imaging characteristics of DDLS in computed tomography (CT) and MRI studies are regularly misconstrued as WDLS, which is largely composed of fat. The dedifferentiated nature is implied by the presence of nodular nonlipomatous foci > 1 cm across. In this patient, we identified a 2.5-cm entirely nonlipomatous mass of intermediate signal intensity in both T1- and T2-weighted MR sequences.

The tell-tale nonadipose foci are best detected and evaluated by MRI. Low-to-intermediate signal intensity in T1-weighted MR images and intermediate-to-high signal intensity in T2-weighted views are characteristic features. Pathologic examination of these foci is critical for proper diagnosis. (6)

To distinguish DDLS from other benign or non-metastasizing fatty growths (ie, lipoma, WDLS), it is important to establish a differential diagnosis. Lipoma is signalled by a mass that uniformly demonstrates fat density on both on CT and MRI, without areas of necrosis or fibrosis. Biopsy is otherwise indicated. Indeed, biopsy documentation of nonfatty constituents is the only means of differentiating DDLS from WDLS. Imaging studies are still helpful in this regard, confirming the mostly fatty substance and perhaps minor nonlipomatous elements of WDLS. In DDLS, nonlipmatous content is extensive and may predominate.

Within the inguinal canal, liposarcomas (37%) and leiomyosarcomas (24%) are the most common fat-bearing malignancies, followed by malignant histiocytic fibromas (10%) and fibrosarcomas (5%). [6]

The patient’s surgical specimen harboured whorled structures similar to nerve sheath tumours and overexpressed the MDM2 gene, qualities suggestive of malignant mesenchymal tumour with spindled cells. Upon consulting a national reference centre, a final diagnosis of DDLS was rendered.

Dedifferentiated liposarcomas are treatable by wide surgical excision, frequently in combination with radiation therapy. Adjunctive chemotherapy may also be given. The overall mortality rate for patients with DDLS is 28-30%.  Such tumours often recur locally, emerging earlier than in instances of WDLS. [7]

The use of imaging to detect and localize potential foci of dedifferentiation helps direct pathologic evaluations and rule out WDLS. This case highlights the importance recognising radiologic hallmarks inherent in soft tissue masses, often signifying specific variants of musculoskeletal liposarcomas.