Imaging description

Long-term lithium therapy (primarily used for treatment of bipolar disorder) commonly results in impaired renal concentrating ability (leading to nephrogenic diabetes insipidus) and occasionally chronic kidney disease due to tubulointerstitial nephropathy. The latter constitutes lithium nephropathy, which is characterized clinically by decreased glomerular filtration rate and pathologically by chronic focal interstitial nephritis with tubular atrophy, parenchymal fibrosis, sclerotic glomeruli, tubular dilatation, and cyst formation [1–4]. The latter can be seen at imaging. The cysts of lithium nephropathy are typically small (1–2 mm), variable in number, and either randomly or primarily cortical in location (Figures 41.1–41.3) [5]. The kidneys may be normal in size or slightly atrophic.

Importance

The finding of abundant, uniform, and symmetrically distributed renal microcysts in normal-sized kidneys in a patient on long-term lithium therapy with renal insufficiency is strongly suggestive of lithium nephropathy and may eliminate the need for diagnostic confirmation by renal biopsy [5].

Typical clinical scenario

The multiple small scattered renal microcysts of lithium nephropathy are usually detected incidentally when a patient on lithium is imaged for unrelated reasons. The appearance is relatively characteristic, and should be correlated with lithium usage. In the largest published series to date, all of 16 patients on long-term lithium therapy with renal impairment demonstrated at least some renal microcysts at MRI [5]. In this series, the degree of renal impairment was variable (creatinine clearances of 20 to 70 mL/min) and all but three of the patients had clinical features of nephrogenic diabetes insipidus.