Leiomyosarcoma of the right iliacus muscle

Clinical History

The patient was admitted to the hospital because of worsening of the general condition with fever, night sweats and weight loss. A CT examination of thorax and abdomen showed a mass in the right iliacus muscle with multiple enlarged right inguinal lymph nodes (LNs) followed by biopsy from the LNs.

Imaging Findings

Figure 1:
An axial CT in the portal venous phase at the pelvic level showing a heterogeneous hypodense mass measuring about 50x30 mm at the lateral part of the right iliacus muscle with irregular enhancing rim.

Figure 2:
Axial CT at the same level in bone window showing evidence of bony erosion of the lateral border of the iliac crest.

Figure 3:
Axial CT at a more caudal level showing a suspicious right inguinal lymph node of about 10 mm with central hypodensity probably due to central necrosis and a marked fat stranding in the soft tissue.

Figure 4:
Coronal CT of the abdomen showing the mass extending from the iliacus muscle into the right inguinal canal.

Discussion

A. Background:
- Leiomyosarcomas are unusual soft-tissue tumours that occur in the retroperitoneum, peripheral soft tissues, gastrointestinal and genito-urinary tracts, vessels and (rarely) in bone. A small number originate in subcutaneous tissues or large vessels, such as the inferior vena cava [1].

B. Clinical presentation:
* Incidence:
-Leiomyosarcoma represents approximately 9% of all soft tissue sarcomas (including retroperitoneum) [3] and is the third most frequently documented sarcoma after malignant fibrous histiocytoma and liposarcoma.

* Age:
-It primarily affects middle-aged to older adults [1].
-Retroperitoneal leiomyosarcomas are more common in women, with peripheral soft tissue or vascular lesions predominating in men [1].

* Location:
-The most common site of origin is the retroperitoneum (20–67% of cases). Approximately 12–41% arise in the peripheral soft tissues, most commonly in the lower extremities [3, 7]. The remainder originate from the genitourinary tract, gastrointestinal tract, trunk or blood vessels.

C. Imaging findings:
-CT is the primary imaging modality for the assessment of abdominopelvic sarcomas and is used in the evaluation of metastatic disease. However, MRI allows a more confident assessment of the site of origin of a mass especially musculoskeletal lesions because of its superior soft-tissue contrast. Gadolinium is used to assess tumour margins, vascularity and vessel involvement [8].

-Masses demonstrate a central low density in keeping with haemorrhage, necrosis or cystic change [5].

-Moderate contrast enhancement is seen at the periphery of the large primary and metastatic lesions [4]. Smaller lesions may be homogeneous [6].

-Metastases from leiomyosarcoma tend to be haematogenously spread. The liver and lung are the most frequent sites (53% and 47% respectively). Soft tissue metastases (23%). Bone metastases (18%). Lymph nodes and/or the gastrointestinal tract (18%). Intraperitoneal seeding to peritoneal and mesenteric reflections occurs from gastrointestinal or mesenteric primary sites.

D. Outcome:
* Management:
-Leiomyosarcomas require detailed evaluation with imaging prior to surgery.
-The radiologist's role is pivotal in assessing the extent of disease with particular attention given to the encasement and/or displacement of adjacent vascular structures and organs.

* Prognosis:
-The prognosis for leiomyosarcoma is poor with an overall 5 year survival rate of 35%. Prognosis is worse for tumours greater than 5 cm and for those arising from the retroperitoneum [2].

E. Take Home Message:
-Leiomyosarcoma is a rare soft-tissue sarcoma with a poor prognosis.
-Retroperitoneal and peripheral soft-tissue tumours are the most common tumours.
-Large, necrotic, heterogeneous soft-tissue masses are usually seen at CT with an isointense signal to muscle on T1w images and an intermediate or high signal on T2w images.

Differential Diagnosis List

Final Diagnosis

Leiomyosarcoma of the right iliacus muscle with metastatic inguinal LN.

URL:	https://www.eurorad.org/case/11578
DOI:	10.1594/EURORAD/CASE.11578
ISSN:	1563-4086