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Published online before print October 19, 2007, 10.1148/radiol.2452061535
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(Radiology 2007;245:848-854.)
© RSNA, 2007

Pediatric Imaging

Tumors in Pediatric Patients at Diffusion-weighted MR Imaging: Apparent Diffusion Coefficient and Tumor Cellularity1

Paul D. Humphries, FRCR, Neil J. Sebire, MD, MRCPath, Marilyn J. Siegel, MD, and Øystein E. Olsen, MD, PhD

1 From the Departments of Radiology (P.D.H., Ø.E.O.) and Histopathology (N.J.S.), Great Ormond Street Hospital for Children NHS Trust, Great Ormond Street, London WC1N 7JH, England; and Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo (M.J.S.). Received September 5, 2006; revision requested November 6; revision received December 6; accepted January 15, 2007; final version accepted March 7. Address correspondence to: Ø.E.O. (e-mail: olseno{at}gosh.nhs.uk).

Purpose: To prospectively assess whether there is a relationship between the apparent diffusion coefficient (ADC) and the histopathologic cell count and whether the ADC can enable differentiation of benign and malignant extracranial mass lesions in children.

Materials and Methods: Institutional ethics approval and parent or guardian consent were obtained. Eleven malignant and eight benign lesions in 19 children (11 girls, eight boys; median age, 3.9 years; age range, 11 days to 15.5 years) who underwent magnetic resonance (MR) imaging of extracranial mass lesions—including a diffusion-weighted sequence (with b values 0, 500, and 1000 sec/mm2)—and histopathologic analysis to prove findings were studied. The median ADC within each mass lesion was compared with the median cell count for 10 high-power microscopic fields in the specimen. The inverse regression between cell count and ADC was calculated. The difference in ADC between benign and malignant lesions was assessed by using the Mann-Whitney U test.

Results: There was an inverse relationship between ADC and cell count, expressed as ADC (in x10–3 mm2/sec) = 0.56 + (66.2/cell count), with a relatively good fit to the observed data (analysis of variance R2 = 0.541, F = 20.0, P < .001). The ADCs of benign lesions ranged from (0.84–2.83) x 10–3 mm2/sec (median, 1.35 x 10–3 mm2/sec; standard deviation, 0.68). The ADCs of malignant lesions ranged from (0.73–1.53) x 10–3 mm2/sec (median, 1.00 x 10–3 mm2/sec; standard deviation, 0.29). There was no significant difference in ADC between benign and malignant lesions (Mann-Whitney U = 22, P = .069). All highly cellular (>150 cells per high-power field) lesions had an ADC lower than 1.5 x 10–3 mm2/sec.

Conclusion: Although there is a significant relationship between cellularity and ADC, cell count probably is not the sole determinant of the ADC. Use of the ADC cannot enable accurate differentiation of malignant and benign lesions.

© RSNA, 2007