Lipofuscin Accumulation in Cortisol-Producing Adenomas With and Without PRKACA Mutations

The adrenal cortex accumulates lipofuscin granules with age. Lipofuscin accumulation is also seen in adrenocortical tumors associated with Cushing syndrome (CS), particularly those with PRKAR1A mutations, such as in primary pigmented nodular adrenocortical disease (PPNAD). We investigated the presence of lipofuscin in cortisol-producing adenomas (CPAs) responsible for CS with and without the PRKACA (pLeu206Arg) somatic mutation. Ten paraffin-embedded sections of CPAs from cases with overt CS with (n=4) and without (n=6) a PRKACA mutation were microscopically examined through three detection methods, the hematoxylin-Eosin (H & E) staining, the Fontana Masson (FM) staining using light microscopy, and lipofuscin autofluorescence, using confocal laser scanning microscopy (CLSM). Sections were examined quantitatively according to the intensity of the pigmentation, as well as qualitatively based on the total number of granular pigments at all visual fields per tissue slide. Tissues from CPAs were compared to peritumoral adjacent tissues (n=5), to Conn adenomas (n=4), and PPNAD (n=3). CPAs had significantly higher number of lipofuscin-pigment granules compared to peritumoral adrenal tissue and Conn adenomas (46.9±9.5 vs. 3.8±4.8, p=0.0001). The presence of the PRKACA mutation did not increase the chances of pigmentation in the form of lipofuscin granules within CPAs associated with CS. Thus, all CPAs leading to CS accumulate lipofuscin, which presents like pigmentation sometimes seen macroscopically but always detected microscopically. PPNAD caused by PRKAR1A mutations is the best known adrenal lesion leading to CS associated with intense lipofuscin pigmentation and this was confirmed here; CPAs harboring PRKACA mutations did not have statistically significantly more pigmentation than CPAs without mutation, but a larger study might have shown a difference.