Fig. 6.6.4 Fig. 6.6.3
Fig. 6.6.2 Fig. 6.6.1
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A 22-year-old man presented with a painless, tender mass in the upper left supracla- vicular region.
Comments Liposarcoma is a malignant tumor of mesenchymal origin. The term liposarcoma does
not imply that the tumor is derived from fat, but rather that the tumor tissue contains dif- ferentiated adipose tissue. Liposarcoma is the second most common soft-tissue sarcoma seen in adults (10–18%) after malignant fi brous histiocytoma. Liposarcomas are classifi ed into four histologic subtypes: well differentiated, myxoid, round cell, and pleomorphic.
Well-differentiated liposarcoma is synonymous with atypical lipoma. Between 40 and 65% of liposarcomas of the extremities occur in the thigh. Other common sites, in the order of descending frequency, are the upper arm and shoulder, popliteal fossa and lower leg, buttocks, and forearm. Clinically, these tumors manifest as painless masses.
The radiological features of a liposarcoma depend on the histological type and tend to refl ect its degree of differentiation. CT or MRI fi ndings for well-differentiated liposarco- mas closely resemble those of subcutaneous fat or a simple lipoma. They are frequently composed of more than 75% fat, while the other types usually have less than 25%.
On CT a well-differentiated liposarcoma may appear as a well-delineated mass, with attenuation values equal to those of simple fat, mimicking a benign lipomatous tumor.
On MRI a well-differentiated liposarcoma shows some thickened linear or nodular soft-tissue septa that enhance after intravenous administration of contrast material.
These small nonlipomatous components are of low signal intensity on T1-weighted im- ages and increased signal intensity on T2-weighted images with fat suppression.
Features for discriminating a well-differentiated liposarcoma from a simple lipoma include a deep (intramuscular) rather than subcutaneous location, a size of more than 10 cm in maximum diameter, the presence of nodular nonadipose components or thick septa, high signal intensity of septa or nodular soft-tissue areas on T2-weighted fat sup- pression or STIR images, and contrast-enhancement of nonadipose components (best seen on fat-suppressed T1-weighted images)
Imaging Findings MRI is the most specifi c modality for diagnosing liposarcoma. Figure 6.6.1 shows an axial
T1-weighted image of a large mass located in the left supraclavicular region, posterior to the sternocleidomastoideus muscle and medial to the scalene muscles and brachial plexus. The tumor is predominantly isointense to subcutaneous fat. Multiple thickened septa extend throughout the tumor (dotted arrow).
On axial T2-weighted MR image the signal intensity of the tumor is similar to that of subcutaneous fat (Fig. 6.6.2) with thick, low signal intensity septa (arrow).
Coronal STIR MR (Fig. 6.6.3) shows the nonadipose areas with increased signal inten- sity relative to fat (open arrowhead).
Axial T1-weighted fat-suppression MR image (Fig. 6.6.4) obtained after contrast ad- ministration shows moderate heterogeneous enhancement of the nonadipose areas (arrowhead).
Case 7 Chordoma
Fig. 6.7.1 Fig. 6.7.2
Fig. 6.7.3
Fig. 6.7.4
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A 54-year-old man had severe low back pain of several weeks’ duration. The pain radiated to both legs. The medical history and physical examination were unremarkable.
Comments Chordoma is the most common primary malignant sacral tumor and accounts for 2–4%
of malignant osseous neoplasms. Chordomas arise from the fetal notochord, which is nor- mally replaced by mesodermal tissue by the 7th week of development. Scattered vestiges of notochord may be found in the nucleus pulposus and can be present at any level from the skull base to the coccyx. Fifty to 60% of chordomas develop in the sacrococcygeal region. These tumors are found at all ages. The mean age at diagnosis is the 6th decade.
Chordoma is more common in males by a 2:1 ratio.
The classic appearance of chordoma is a destructive, lytic lesion, commonly with inter- nal calcifi cations (30%). A large presacral soft-tissue component is usually present. These tumors are capable of extending across the adjacent disk space and the sacroiliac joint.
Chordoma shows heterogeneous low signal intensity on T1-weighted images and promi- nent heterogeneous increased signal intensity on T2- weighted MR images, refl ecting the high water content of the lesions. Contrast enhancement at MR imaging is common.
The differential diagnosis includes other primary tumors (sarcoma, giant-cell tumor, and, rarely, ependymoma). Metastases are the most common sacral neoplasm.
The treatment of chordoma is surgical. Total surgical resection provides the best hope for cure. MR imaging has proven highly accurate for evaluating the extent of disease. The majority of patients succumb to locally recurrent tumor because chordoma is relatively radioresistant, although patients with chordoma often survive many years after surgery.
The 5-year survival in patients treated with radiation therapy is 50%.
Imaging Findings Plain radiography of the sacrum is nonspecifi c and might reveal a lytic lesion, with
obliteration of the cortex (dotted arrow) (Fig. 6.7.1).
CT is useful to detect the internal calcifi cations (arrow) (Fig. 6.7.2) and the extent of the destructive soft-tissue mass within the sacrum. In this case, the mass extends across the sacral canal and the anterior neuronal foramina.
MRI is the best imaging technique, showing on sagittal T1-weighted images low sig- nal intensity, and marked enhancement after contrast administration with a peripheral septal pattern (open arrowhead) (Fig. 6.7.3). T2-weighted MR image (Fig. 6.7.4) shows a heterogeneously (due to the presence of septa) hyperintense sacral mass with a presacral and soft-tissue component within the canal.