Diffusion tensor imaging and fiber tractography of the epididymis in men with non-obstructive azoospermia.

Background: Scrotal magnetic resonance imaging, including diffusion tensor imaging and fiber tractography has emerged as a valuable, non-invasive method in the evaluation of non-obstructive azoospermia. The epididymis has a crucial role in male infertility.

Objectives: To evaluate the role of diffusion tensor imaging and fiber tractography of the epididymis in the work-up of non-obstructive azoospermia.

Materials and methods: This prospective study included 22 men with non-obstructive azoospermia and 15 controls. Scrotal magnetic resonance imaging, including diffusion tensor imaging, was performed. The epididymal apparent diffusion coefficient and fractional anisotropy were measured. Fiber tractography reconstructions were created. Non-parametric statistics compared apparent diffusion coefficient and fractional anisotropy of the epididymis between: (1) non-obstructive azoospermia and normal men; (2) histologic phenotypes of non-obstructive azoospermia; (3) non-obstructive azoospermia men, with positive and negative sperm retrieval; and (4) non-obstructive azoospermia men, with idiopathic and non-genetic etiology. Visual assessment of the epididymal fiber tracts was performed.

Results: Lower epididymal fractional anisotropy (p = 0.027) was observed in men with non-obstructive azoospermia in comparison to normal population. Fractional anisotropy decreased (p = 0.033) in cases with idiopathic non-obstructive azoospermia in comparison to men with non-genetic etiology. Fiber tractography showed abnormalities in epididymal fiber tracts in men with non-obstructive azoospermia, including decrease in number and/or thickness and disorganization. However, diffusion tensor imaging parameters were unable to differentiate the histologic types of non-obstructive azoospermia and to predict the results of sperm retrieval (p > 0.05).

Discussion and conclusion: Our preliminary observations showed that diffusion tensor imaging and fiber tractography of the epididymis provide valuable, non-invasive biomarkers in the work-up of non-obstructive azoospermia, although the clinical significance of these findings is yet to be determined. However, diffusion tensor imaging data were not predictive for the presence of spermatozoa before microdissection testicular sperm extraction.