Apparent Diffusion Coefficient Values Not Helpful for Diagnosing Adrenal Neoplasms

The objective of a recent study was to determine if diffusion-weighted MRI is helpful in the differential diagnosis of adrenal neoplasms.

Apparent diffusion coefficient (ADC) values are not useful in the differentiation of benign from metastatic adrenal lesions.

Design

Retrospective analysis.

Participants
Forty-two patients (24 men, 18 women) with adrenal tumors diagnosed on MRI. All patients had either pathological confirmation or follow-up imaging performed. One patient had bilateral adrenal tumors.

Methodology
Adrenal lesions were initially detected at time of a CT examination performed for various other indications. There were 31 adenomas, 7 metastases, and 5 pheochromocytomas. The primary extra-adrenal tumors were pancreas and lung.

MRI was performed with a 1.5-T system. Imaging sequences included T2-weighted half-Fourier acquisition single-shot turbo spin-echo, dual-echo in-and out-of-phase gradient echo, and single-shot echo-planar diffusion-weighted images with fat suppression.

The signal intensity index (SII) was calculated by subtracting the region of interest (ROI) value of the lesion on the out-of-phase from the value found on in-phase images, then that result was divided by the in-phase ROI value, and subsequently multiplied by 100. Diffusion-weighted images were obtained with b values of 0 and 1000 s/mm2. ADC value calculations were also performed.

Results
All tumors were high-signal intensity on diffusion-weighted images. Lesions ranged in size from 0.8 to 11.0 cm without a characteristic dimension for any individual tumor type. There was no significant difference found between ADC values of adenomas and metastatic lesions, while pheochromocytomas showed higher ADC values than adenomas and metastatic lesions.

There was a higher mean SII found with adenomas than with metastatic lesions or pheochromocytomas. There were no characteristic ADC values or SII measurements to help differentiate between a non-functioning adenoma, aldosteronoma, and Cushing adenoma.

Reviewer’s Comments
The results of this study are useful in demonstrating that, while pheochromocytomas showed higher ADC values, there was no useful ADC value to help distinguish between adenomas and metastatic lesions.

Therefore, diffusion-weighted MRI and ADC values should not be used alone, but rather as a supplement to information provided by other sequences in the standard MRI protocol. One of the limitations reported in this study was the small number of adrenal tumors included.

Author: John C. Sabatino, MD, MSD

Reference:
Tsushima Y, Takahashi-Taketomi A, Endo K. Diagnostic Utility of Diffusion-Weighted MR Imaging and Apparent Diffusion Coefficient Value for the Diagnosis of Adrenal Tumors. J Magn Reson Imaging; 2009;29; (January): 112-117: