A contribution to the morphology and pathogenesis of thyroid-like lesions in the kidney.

The morphological variations of thyroid-like lesions in the kidney in 15 cases with chronic destructive interstitial nephritis as the basic alteration were examined with light microscopy and immunohistological methods. Reflux pyelonephritis was present in some cases. Thyroid-like lesions can develop at any age. "Mature" thyroid-like lesions possess large follicular structures and solid tubular epithelial cell complexes, whereas the follicular structures in "young" thyroid-like lesions are small. The hyaline casts are Tamm-Horsfall protein positive in between one- and two-thirds of the follicles. IgA is present in all follicular lumina. The thyroid-like lesions are the result of a regenerative process. They develop after subtotal parenchymal destruction of remaining tubular epithelial cells from the ascending limb of the loop of Henle, the distal convoluted tubules and the collecting ducts. They are pathognomonic for healed destructive bacterial interstitial nephritis, but can also be observed in analgesic nephropathy, hydronephrosis, and nephronophthisis when these basic diseases are preceded by pyelonephritis.