Hypothalamic hamartomas: Correlation of MR imaging and spectroscopic findings with tumor glial content

Abstract

Background and purpose: There is variability in the literature concerning the appearance and histology of hypothalamic hamartomas. This study correlates the MR imaging and proton MR spectroscopic properties of hypothalamic hamartomas with histopathologic findings.

Methods: Studies were performed with 3T and 1.5T scanners. Single voxel hamartoma spectra were acquired by using short-echo-time point-resolved spectroscopy sequences (PRESS). 2D PRESS chemical shift imaging (CSI) spectroscopic sequences were also obtained for comparison of tumor-derived spectra with normal gray matter of the amygdala. Sequences were used to compare choline (Cho), N-acetylaspartate (NAA), and myoinositol (mI) resonances by using a creatine (Cr) reference. Spectral ratios and T2 signal intensity ratios of the hamartomas were then compared with histopathologic findings.

Results: Data from single voxel spectroscopic sequences demonstrated a statistically significant decrease in NAA/Cr and an increase in mI/Cr ratios in tumor tissue when compared with values in normal gray matter of the amygdala. In addition, Cho/Cr ratios were also increased when compared with those in normal gray matter controls. Among the 14 hamartomas sampled, a spectrum of increased mI/Cr ratios was seen. Those tumors with markedly elevated mI/Cr demonstrated an increased glial component when compared with the remaining tumors. Increased glial component was also found to have a positive correlation with hyperintensity of lesions on T2-weighted images.

Conclusion: We have identified a correlation between the glial/neuronal fraction as determined by histopathology and MR spectral and T2 hyperintensity variations among hypothalamic hamartomas.

Fig 1.

Photomicrograph (H&E stain) from predominantly neuronal hypothalamic hamartoma (A) with corresponding single voxel MR spectrum (3T) and axial T2-weighted image (B, -C). The mI peak is moderately elevated and tumor is slightly hyperintense relative to gray matter on T2-weighted images. Also shown are a photomicrograph from a predominately glial hamartoma (D) with corresponding spectrum (1.5T) and T2-weighted images (E,-F). The mI peak is markedly elevated, and the lesion is very hyperintense in comparison to gray matter. Cho is mildly elevated, and NAA is reduced in both cases.

Fig 2.

Graph shows the comparison of spectral ratios within tumor and normal gray matter. A significant decrease is noted in NAA/Cr in the hypothalamic hamartomas compared with normal controls. Significant increases are seen in mI/Cr and Cho/Cr. Horizontal dashes represent 95% confidence intervals.

Fig 3.

Scatterplot shows individual mI/Cr ratios of hypothalamic hamartomas versus 6-point pathology rating scale (1 = mostly neuronal, 6 = mostly glial). Samples exhibit increased mI concentrations with increasing glial content. One relatively neuronal sample (pathology rating, 2) demonstrates an anomalously high mI/Cr = 1.1.

Fig 4.

Graph shows relative T2 hyperintensity of hypothalamic hamartomas versus 6-point pathology rating scale (1 = mostly neuronal, 6 = mostly glial). Data demonstrate increasing T2 intensity with increased tumor glial content. A sample with pathology rating of 2 and an anomalously high T2 ratio of 1.8 is the same sample seen as an outlier in Fig 3 and discussed in the text.