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Minimum ADC Values Helpful in Detecting Apparent High-Grade Astrocytomas

March 24, 2009
Written by: , Filed in: Neuroradiology
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Minimum ADC Values Helpful in Detecting Apparent High-Grade Astrocytomas

In general, higher grade astrocytomas demonstrate increased enhancement, necrosis, and heterogeneity compared with low-grade lesions.

However, there can be a great deal of overlap, and some high-grade lesions can have features typical of low-grade tumors.

Higher grades have also been demonstrated to have greater restriction of diffusion, ie, lower apparent diffusion coefficient (ADC) values, than low-grade astrocytomas.

A recent study was conducted to determine whether minimum ADC values have diagnostic value for preoperative evaluation of supratentorial astrocytomas that have the features of low-grade astrocytomas.

The study results, published in The American Journal of Neuroradiology, have found that in assessing low-grade-appearing cerebral neoplasms, the assumption that a minimum apparent diffusion coefficient of ≤1.055 is actually high grade will result in 87.5% sensitivity and 79.0% specificity.

The Study
Of 118 patients with grades II-IV astrocytomas, MRI examinations were evaluated to find those with supratentorial lesions with low-grade features, including little or no mass effect, vasogenic edema, and little or no contrast enhancement.

Sixteen patients were identified, 8 of whom had low-grade and 8 of whom had high-grade histopathologic diagnosis (6 with grade III and 2 with grade IV).

Methodology
All MRIs were performed within 1 month of surgery. MRIs included FLAIR, T1, T2, and contrast-enhanced T1. Five-mm diffusion-weighted images were obtained in 3 planes with b-values of 0 to 1000 s/mm2. Forty-mm2 regions of interest were placed throughout each lesion to determine the minimum ADC for each lesion.

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review

Results of the Study
Median mADC for the high-grade group (group B) was 1.035 x 10-3 mm2sec-1, which was significantly lower than that of the low-grade group A, which was 1.19 (P =0.021).

No high-grade lesions were above 1.25, whereas 2 low-grade lesions were.

No low-grade lesions were below 1.0, but 2 high-grade lesions were.

Receiver operating characteristic (ROC) analysis demonstrated that using a cut-off value of 1.055 for the mADC would result in 87.5% sensitivity and 79.0% specificity in detecting high-grade lesions (P =0.021).

Conclusions
There is an inverse correlation between the minimum ADC values and grading of supratentorial astrocytomas with typical MRI features of low-grade lesions that can aid in preoperative grading of astrocytomas.

Reviewer’s Comments
This study suggests that minimum ADC can be added to the list of potential methods for determining the grade of astrocytomas preoperatively.

The advantage of ADC is that it is now considered routine at many centers and is thus readily available.

The authors point out that minimum ADC might also be used to determine the site of biopsy of the lesion, as many gliomas have regional differences in histology.

Author: Yaron Lebovitz, MD

Reference:
Lee EJ, Lee SK, et al. Preoperative Grading of Presumptive Low-Grade Astrocytomas on MR Imaging: Diagnostic Value of Minimum Apparent Diffusion Coefficient. Am J Neuroradiol; 2008;29 (November-December): 1872-1877

Neuroradiology Review

The Johns Hopkins University School of Medicine
Course Directors: David Yousem, MD, MBA and Doris Lin, MD, PhD Maintaining certification requires not only medical knowledge to deliver quality care but also other essential elements that must be developed and maintained throughout every radiologist’s career. Therefore, this program serves as a comprehensive review of neuro-radiology and prepares the participants to tackle imaging of the brain, spine, head and neck, as well as the vascular anatomy of the central nervous system. Click here to read more or order: Neuroradiology Review
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