First published online August 6, 2007
British Journal of Radiology (2008) 81, 73-81
© 2008 British Institute of Radiology
doi: 10.1259/bjr/18595145
Radiological imaging features of non-uterine leiomyosarcoma
P J O'Sullivan, MRCPI, FFR, RCSI,
A C Harris, FRCR and
P L Munk, MDCM, FRCPC
Department of Radiology, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada V5Z 1M9
Correspondence: Dr Paul J O'Sullivan, Department of Diagnostic Radiology — Unit 371, MD Anderson Cancer Center, University of Texas, 1515 Holcombe Boulevard, Houston, Texas 77030–4009, USA. E-mail: paul.o'sullivan{at}di.mdacc.tmc.edu
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Abstract
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Leiomyosarcomas are unusual soft-tissue tumours that occur in the retroperitoneum, peripheral soft tissues, gastrointestinal and genito-urinary tracts, vessels and (rarely) in bone. The aim of this pictonal review is to delineate the more specific radiological features that would suggest a radiological diagnosis of leiomyosarcoma prior to biopsy.
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Introduction
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Leiomyosarcoma is an uncommon malignant neoplasm of smooth muscle arising from many sites, including the peripheral soft tissues, retroperitoneum, gastrointestinal tract, genitourinary system and, rarely, bone. A small number originate in subcutaneous tissues or large vessels, such as the inferior vena cava (IVC).
CT is the primary imaging modality for the assessment of abdominopelvic sarcomas and is used in the evaluation of metastatic disease. However, MRI is also utilized for its multiplanar capabilities, which allow a more confident assessment of the site of origin of a mass, in particular within the pelvis, and its involvement with local structures. Musculoskeletal lesions are primarily evaluated with MRI because of its superior soft-tissue contrast and better definition of tumour boundaries.
The aim of this manuscript is to present the imaging features of non-uterine leiomyosarcoma utilizing CT and MRI, indicating findings that may help to differentiate these tumours from other sarcomas.
Clinical features
Leiomyosarcoma represents approximately 9% of all soft tissue sarcomas (including retroperitoneum) [1] and is the third most frequently documented sarcoma after malignant fibrous histiocytoma and liposarcoma.
Leiomyosarcoma primarily affects middle-aged to older adults. Retroperitoneal leiomyosarcomas (Figure 1
) are more common in women, with peripheral soft tissue or vascular lesions predominating in men. In the retroperitoneum, tumours may present with an abdominal mass, pain, swelling, weight loss or lower extremity oedema.
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Figure 1. A 75-year-old woman with large inoperable retroperitoneal leiomyosarcoma. (a) Axial post-contrast CT shows marked internal vascularity. (b) The tumour invades the left renal vein (arrow). (c) Tumour extension via the inferior vena cava to the right atrium (arrow).
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Classification
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The majority of lesions originally thought to represent leiomyosarcomas arising from the gastrointestinal tract are now classified as gastrointestinal tumours (GISTs) with the use of the immunohistochemical markers for the c-kit (CD117) proto-oncogene [2].
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Location
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The most common site of origin is the retroperitoneum (20–67% of cases) (Figure 2). Approximately 12–41% arise in the peripheral soft tissues, most commonly in the lower extremities [1, 3]. The remainder originate from the genitourinary tract (Figures 3 and 4), gastrointestinal tract, trunk or blood vessels.
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Figure 2. A 52-year-old man with leiomyosarcoma of the prostate: large heterogeneous mass with central necrosis invading the bladder and abutting the anterior wall of the rectum.
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Figure 3. An 80-year-old man with multiple, rounded, pulmonary metastatic nodules seen in leiomyosarcoma.
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Figure 4. A 61-year-old woman with large retroperitoneal leiomyosarcoma. (a) Axial post-contrast CT shows extensive tumour encasing the aorta and inferior vena cava. (b) Multiple liver metastases with peripheral rim enhancement and central necrosis. (c) A lytic metastasis to the left ilium is also seen.
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Lesions are often large at presentation (Figures 5 and 6) because of the compliance of the retroperitoneal space and the ability of the tumour to infiltrate between organs.
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Figure 5. A 70-year-old woman with leiomyosarcoma of the right ureter. (a) Axial post-contrast CT shows a round heterogeneously enhancing mass in the position of the distal right ureter (arrow). (b) Large necrotic hepatic metastases are often seen in leiomyosarcoma.
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Figure 6. A 68-year-old woman with leiomyosarcoma of the mesentery. (a) Axial post-contrast CT shows a lobulated heterogeneous mass in the small bowel mesentery. (b) Enhancing metastases above iliac vessels (white arrow) and necrotic metastasis to the right iliacus (black arrow). (c) Serosal metastasis to the right round ligament (curved arrow).
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Extremity tumours (Figures 7, 8 and 9) present as painless slow-growing masses, which may appear clinically benign. Pain is a presenting feature in primary leiomyosarcoma of bone, which most frequently involves the femora, tibia (Figures 10 and 11) and ilia [4].
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Figure 7. A 67-year-old man with leiomyosarcoma of the anterior compartment of the thigh. Sagittal T1 (a), sagittal T2 (b) and axial T2 (c) MR images with fat saturation demonstrate the large, multiloculated anterior compartment mass within the deep soft tissues. Images courtesy of Dr L M White, Mt Sinai Hospital, Toronto, ON.
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Figure 8. A 62-year-old woman with leiomyosarcoma of the medial distal thigh. (a) Coronal T1 image shows a uniform, low-signal, soft tissue tumour (arrow). (b) Coronal T2 image demonstrates a heterogeneous signal. (c) Axial T1 fat-saturation image shows heterogeneous enhancement following gadolinium.
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Figure 9. A 55-year-old woman with leiomyosarcoma of the medial right upper thigh. (a) T1 axial image demonstrates a homogeneous lesion isointense to muscle. (b) Axial T2 image shows areas of intermediate signal relative to fat. (c) Coronal short tau inversion recovery (STIR) image shows uniform high-signal intensity with thin internal septations.
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Figure 10. A 23-year-old man with leiomyosarcoma of the distal femur. (a) Anteroposterior radiograph shows a permeative lytic lesion of the distal femoral metaphysis extending to the epiphysis. (b) Axial T1 weighted image shows replacement of the marrow cavity with homogeneous hypointense tumour and a small area of cortical breakthrough laterally. (c) Axial T2 weighted image shows areas hypointense to fat. (d) Coronal short tau inversion recovery (STIR) image shows a diffuse high signal.
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Figure 11. A 56-year-old man with leiomyosarcoma of the tibia. (a) Sagittal T1 weighted MR image shows linearly orientated tumour occupying the proximal diaphysis of the tibia. (b) The tumour is hyperintense on this sagittal T2 weighted image with fat saturation demonstrating extension into the soft tissues. (c) Axial T1 fat-saturation image post-gadolinium shows tumour enhancement with cortical permeation and an adjacent soft tissue component. Images courtesy of Dr L M White, Mt Sinai Hospital, Toronto, ON.
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Imaging features
Cross-sectional imaging allows a detailed evaluation of the size and extent of the tumour. In the abdomen and pelvis, CT with oral and intravenous contrast enhancement demonstrates which compartments of the retroperitoneum and mesentery are involved and which vessels and organs are encased (Figure 4a
) or displaced [5].
Retroperitoneal leiomyosarcomas are often large (average 11 cm diameter in one series) and heterogeneous (Figures 1a and 4a) [6]. Masses demonstrate a central low density in keeping with haemorrhage, necrosis or cystic change [2]. Moderate contrast enhancement is seen at the periphery of the large primary and metastatic lesions [5], whereas smaller lesions may be homogeneous [6]. Liver metastases are well defined with central necrosis. Calcification is uncommon but has been reported [2].
The multiplanar capabilities of MRI are particularly useful in determining more precisely the site of tumour origin and involvement of adjacent structures (Figure 10). Gadolinium is used to assess tumour margins, vascularity and vessel involvement [7].
MRI is the imaging modality of choice for evaluation of peripheral soft tissue tumours. Leiomyosarcoma has a non-specific appearance on MRI, revealing a non-fatty mass (Figures 7 and 8). Large deep lesions tend to be heterogeneous with areas of necrosis. Superficial lesions, which are usually smaller, may be homogeneous.
Tumours arising from large vessels, commonly the IVC, femoral vein or greater saphenous vein, are intraluminal, extraluminal or a combination of both. These lesions are well defined, may expand the vessel lumen and appear isointense to muscle on T1 and hyperintense on T2 weighted images [8].
Primary leiomyosarcoma of bone is purely osteolytic with aggressive features such as endosteal scalloping, permeation, poor definition of margins and lack of sclerosis on conventional radiographs [4]. Lesions of the long bones involve the metaphysis, often with extension into the diaphysis or epiphysis (Figure 10). The tumour is primarily intramedullary in origin and may extend into the soft tissues, typically with a subtle periosteal reaction (Figure 11). Lesions occupy a significant length of bone (average 11 cm in one series) [4].
On MRI the tumour is clearly defined. It is isointense to muscle on T1 weighted imaging (Figures 9a and 11a), intermediate to hypointense to fat on spin-echo T2 weighted imaging (Figure 9b) and predominantly hyperintense on spin-echo T2 imaging with fat saturation (Figure 9c) [4]. It is postulated that the intermediate-to-low signal on T2 weighted imaging is caused by a fibrous or muscle component; this is not a common feature of other osteolytic lesions.
Because this is a rare tumour, an extraosseous primary site, often uterus, must be excluded before a definite diagnosis of primary leiomyosarcoma of bone is reached.
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Metastases
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Metastases from leiomyosarcoma tend to be hematogenously spread. The liver and lung are the most frequent sites, with metastases at these sites occurring in 53% and 47% of patients respectively (Figures 3 and 4b). Soft tissue metastases occur in 23% of patients. Metastases to bone (Figure 4c) are seen in 18% of cases. Lymph nodes and/or the gastrointestinal tract are a site of metastatic disease in a further 18% of patients. Intraperitoneal seeding to peritoneal and mesenteric reflections occurs from gastrointestinal or mesenteric primary sites (Figure 6). Local tumour recurrence may be seen at the site of previous surgery.
Deep intra-abdominal, retroperitoneal and large vein tumours have the most frequent occurrence of metastases (40–50%). Tumours occurring in subcutaneous tissue produce metastases in approximately 30% of patients, whereas superficial epidermal lesions rarely produce metastases [9].
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Staging and surveillance imaging
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In our department, we perform a dynamic contrast-enhanced CT scan of the thorax, abdomen and pelvis with a hepatic portovenous phase to rule out pulmonary and hepatic metastases at our initial staging evaluation. Subsequent imaging of patients with leiomyosarcoma depends on the primary tumour site, the likely sites of recurrence and therapy.
In patients with a primary intra-abdominal or pelvic lesion, we perform a contrast-enhanced CT scan of the abdomen and pelvis every 6 months for 1 year and then annually thereafter. A chest radiograph is also taken at each visit in those without initial pulmonary metastases. In those with pulmonary metastases at presentation, a CT scan of the thorax is also performed. Some institutions advocate a CT scan of the thorax for all patients at follow-up imaging visits.
Ultrasound is not routinely used for recurrence surveillance in our institution, as it has a lower sensitivity in detecting bowel, retroperitoneal or mesenteric recurrences. It is useful, however, in directly evaluating primary or recurrent cutaneous lesions and lymph nodes. These lesions tend to be small, homogenous and hypoechoic. A biopsy can be performed simultaneously for definitive evaluation. We do use ultrasound for evaluating CT-detected hepatic lesions and directing biopsies. These hepatic lesions tend to be large and hypoechoic because of extensive central necrosis.
CT is the primary mode of follow up in our institution because of an increased ease of access. Gadolinium-enhanced MRI can also be used if available. However, we do routinely perform a pelvic MRI in the setting of hepatic leiomyosarcoma metastases of unknown origin detected in a female patient in order to rule out a uterine leiomyosarcoma.
Positron emission tomography has a demonstrated use in imaging of uterine leiomyosarcomas; however, we were not able to identify any current literature describing its use in non-uterine leiomyosarcomas.
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Differential diagnosis
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The main differential diagnosis for leiomyosarcomas includes GISTs, large necrotic lymphomas and primitive neuroectodermal tumours (PNET).
GISTs were previously grouped under leiomyosarcomas. However, with the advent of immunohistochemistry they have been reclassified as GISTs as they show expression of c-kit (CD117) and a subsequent chemotherapeutic response to tyrosine kinase inhibitors.
Similarly to leiomyosarcomas, intra-abdominal and pelvic GIST tumours are often large (more than 10 cm) at presentation, with heterogeneous enhancement and central necrosis. They also can occur in the mesentery, omentum and retroperitoneum. Hematogenous spread to the liver, producing cystic metastases, and lung also occurs. GIST tumours, however, more commonly occur in a submucosal or intraluminal position in the stomach, jejunum and ileum whereas leiomyosarcomas are more common in the retroperitoneum and soft tissues.
Lymphoma should also be considered in the differential diagnosis when a large mass with a necrotic centre is encountered in the abdomen or pelvis.
PNETs are rare in the abdomen but can occur in an intravascular location as with leiomyosarcomas. PNETs have also been reported in the small bowel mesentery and abdominal wall. They too are often large at presentation, with a heterogeneous enhancement pattern [10].
The three lesions described above have a "non-specific" appearance similar to leiomyosarcoma, which necessitates a tissue diagnosis. This is relevant as all three are chemosensitive whereas leiomyosarcoma is relatively insensitive to chemotherapy.
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Prognosis
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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 [11].
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.
Following consultation with an oncologic surgeon, core biopsy is performed under ultrasound or CT guidance. Our practice is to perform a pre-excision biopsy in each case, as other more chemosensitive lesions such as lymphoma or PNET may mimic leiomyosarcoma. Reduction in tumour bulk may be achieved with pre-operative chemotherapy in these lesions, facilitating a more adequate surgical excision. In addition, the biopsy route is planned with the oncologic surgeon, and complete excision of the biopsy tract is included at the time of tumour resection, removing the possibility of tumour seeding at the biopsy tract.
Definitive treatment comprises early resection with wide margins. In the retroperitoneum this frequently includes adjacent organs such as the colon, small bowel, kidney, adrenal and pancreas. Even after adequate surgical excision, there is a high incidence of recurrent disease.
Primary radiation for cure is seldom effective for retroperitoneal leiomyosarcomas but can provide palliation in select cases [12]. Radiation is used before or after excision of large musculoskeletal tumours depending on tumour site and excision margins.
The role of adjuvant chemotherapy is still unclear as leiomyosarcomas are not particularly chemosensitive. Close clinical monitoring in conjunction with regular scanning with either CT or MRI is recommended, as recurrent disease may be amenable to salvage therapy.
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Conclusions
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Leiomyosarcoma is a rare soft-tissue sarcoma with a poor prognosis, most common in middle-aged to elderly woman. 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 T1 weighted images and an intermediate or high signal on T2 weighted images. Liver and pulmonary metastases are commonly seen.
Received for publication January 11, 2006.
Revision received April 12, 2006.
Accepted for publication April 25, 2006.
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Abstract
Introduction
