Posttherapeutic intraaxial brain tumor: the value of perfusion-sensitive contrast-enhanced MR imaging for differentiating tumor recurrence from nonneoplastic contrast-enhancing tissue

Abstract

Background and purpose: Differentiation of tumor recurrence from treatment-related changes may be difficult with conventional MR imaging when newly enhancing lesions appear. Our aim was to determine the value of perfusion-sensitive contrast-enhanced MR imaging for differentiating recurrent neoplasm from nonneoplastic contrast-enhancing tissue.

Methods: Twenty patients in whom new enhancing lesions developed within irradiated regions were examined prospectively with perfusion-sensitive contrast-enhanced MR imaging. Twelve of them also underwent thallous chloride Tl 201 single-photon emission tomography (201Tl-SPECT). Normalized relative cerebral blood volume (rCBV) ratios and thallium indexes were evaluated to determine whether the new enhancing lesions were recurrent or not. Five instances of tumor recurrence and one of radiation necrosis were verified histologically; in the others, tumor recurrence was distinguished by lesions that progressively increased in size on serial MR examinations over at least 5 months, and nonneoplastic contrast-enhancing tissue was distinguished by lesions that disappeared or decreased in size on serial MR studies over at least 9 months.

Results: When normalized rCBV ratios were higher than 2.6 or lower than 0.6, enhancing lesions were either recurrent (n = 5) or nonneoplastic contrast-enhancing tissue (n = 3), respectively. All nonneoplastic contrast-enhancing tissue had a low thallium index, whereas three of four recurrent lesions had a high index.

Conclusion: An enhancing lesion with a normalized rCBV ratio higher than 2.6 or lower than 0.6 may suggest tumor recurrence or nonneoplastic contrast-enhancing tissue, respectively. In these cases, further examination with 201Tl-SPECT may not be necessary. However, when the normalized rCBV ratio is between 0.6 and 2.6, 201Tl-SPECT may be useful in making the differentiation.

FIG 1. 63-year-old woman with a recurrent anaplastic astrocytoma verified by surgical resection. A, Contrast-enhanced T1-weighted MR image (690/14/1; section thickness, 5 mm) shows a focally enhancing area (arrow) with a surrounding nonenhancing zone of low intensity and mass effect in the right frontal lobe. B, Anaplastic astrocytoma appears as an area of hyervascularity (arrow) on rCBV map (normalized rCBV ratio, 4.45). C, Histologic specimen shows densely accumulated tumor cells (hematoxylin-eosin, original magnification × 200).

FIG 2. 78-year-old man with a recurrent glioblastoma. The diagnosis was determined by the progressively enlarging area of enhancement on serial MR images and by the patient's clinical deterioration. A, Contrast-enhanced T1-weighted MR image (690/14/1; section thickness, 5 mm) shows inhomogeneous enhancement (arrows) with surrounding nonenhancing zone of low intensity and mass effect in the right temporoparietal lobe. B, The recurrent tumor is seen as an area of hypovascularity (arrows) on the rCBV map (normalized rCBV ratio, 0.83). C, ²⁰¹Tl-SPECT scans show abnormal uptake in the area of recurrent tumor (arrow), consistent with tumor recurrence.

FIG 3. 29-year-old man with radiation necrosis (verified by stereotactic biopsy) who had undergone subtotal tumor resection followed by conventional radiation therapy (60 Gy) and systemic chemotherapy 26 months earlier. Ten months later, tumor recurrence was found, and was treated by subtotal resection and chemotherapy. A, Contrast-enhanced T1-weighted MR image (690/14/1; section thickness, 5 mm) shows enhanced area (arrow) within surrounding nonenhancing zone of low intensity and mass effect in the left temporal lobe. B, Radiation necrosis appears as an area of hyovascularity (arrow) on the rCBV map (normalized rCBV ratio, 0.56). C, Histologic specimen shows avascular areas, consistent with radiation necrosis (hematoxylin-eosin; original magnification × 200).

FIG 4. 49-year-old man without tumor recurrence. The diagnosis was based on the decreasing size of the enhanced area on serial MR images. A, Contrast-enhanced T1-weighted MR image (690/14/1; section thickness, 5 mm) shows a small focus of enhancement (arrow) within surrounding nonenhancing zone of low intensity and mass effect in the left frontal lobe. B, Enhanced area appears as a region of hypervascularity (arrows) on the rCBV map (normalized rCBV ratio, 1.79).

FIG 5. 20-year-old woman without tumor recurrence. The diagnosis was based on the disappearance of the enhancing area on serial MR images. A, Contrast-enhanced T1-weighted MR image (690/14/1; section thickness, 5 mm) shows a small focus of enhancement (arrows) within surrounding nonenhancing zone of low intensity and mass effect in the left frontal lobe. B, The enhancing area appears mildly hypervascular (arrows) on the rCBV map (normalized rCBV ratio, 1.17). The effects of previous surgery can be seen as susceptibility artifacts in right frontal region (arrowheads). C, ²⁰¹Tl-SPECT scan shows no abnormal uptake in the enhancing lesion (arrows), consistent with lack of tumor recurrence.

FIG 6. Relationship between normalized rCBV ratios in patients with tumor recurrence and those with nonneoplastic contrast-enhancing tissue

FIG 7. Relationship between thallium indexes in patients with tumor recurrence and those with nonneoplastic contrast-enhancing tissue