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Identification of Target Sign and Diagnosis of Schwannomas
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Posted on: 11/15/2007
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Schwannomas, benign (not cancerous) tumors that affect the peripheral nerves, make up about 10 percent of cases of soft tissue tumors. Their correct diagnosis is important because schwannomas can be mistaken for malignant (cancerous) peripheral nerve sheath tumors. The malignant tumors require that a surgeon remove considerably more tissue when removing them (a wide resection), than does surgery for a schwannoma.
Researchers have found an indicator that may suggest a schwannoma, called a target sign. However, the target sign is also sometimes seen of the malignant tumors.
The authors of this study wanted to see if findings from under the microscope would be backed up with findings from imaging studies, such as magnetic resonance imaging (MRI). The researchers studied the records of 199 schwannomas in 177 patients (76 males), aged between six to 84 years. Eighteen of the patients had several tumors; 59 tumors were in the arms, 94 tumors in the legs, 30 tumors in the trunk, and 16 in other locations. One hundred four were located in the between muscles (intermuscular, 61 in the muscle (intramuscular), 18 beneath the skin (subcutaneous), and 16 elsewhere. These patients were compared with 782 patients who had other soft tumor removed (control group). All patients in the study group, except for 6, had marginal, or limited, resection of the schwannomas. The six other patients had a wide resection because their surgeons suspected that the patients may have a malignant tumor.
Records showed that MRI was performed for all patients, enhanced computed tomography imaging, or CT scans, were performed in 74 cases, and ultrasound in 32.
Upon reviewing the imaging tests and the macroscopic findings, the researchers found that typical schwannomas showed a biphasic (2-sided) pattern that was similar to what the researchers found on the imaging. Of the schwannomas, 162 showed "a biphasic pattern of a central yellowish fibrous area and a peripheral myxoid [mucus-like] area."
The researchers report that they were able to define the target sign by MRI as a distinct mass that corresponded with the biphasic pattern. With this, they believe that this is useful in helping diagnose the presence of a schwannoma.
The study did have some weaknesses, the researchers pointed out. A proportion (11 percent) of the cases were excluded because MRI was not available nor were the researchers able to obtain follow-up clinical data.
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References:
Hideyuki Koga, MD, et al. Definition of the Target Sign and Its Use for the Diagnosis of Schwannomas. In Clinical Orthopaedics and Related Research. November 2007. Vol. 464. pp. 224-229.
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