MON-295 Histopathological Evaluation (HISTALDO) Predicts Outcome in Unilateral Primary Aldosteronism

Abstract Disclosure: T.S. Goldbaum: None. F.L. Ledesma: None. A.G. Guimaraes: None. J. Okubo: None. E.Z. Kawahara: None. V. Calsavara: None. L.A. Bortolloto: None. J.L. Chambo: None. M.B. Fragoso: None. M.A. Pereira: None. A. Pio-Abreu: None. G.V. Silva: None. J.V. Silveira: None. F. Consolim-Colombo: None. L.F. Drager: None. W.C. Nahas: None. A. Latronico: None. B.B. Mendonca: None. M.Q. Almeida: None. M.N. Zerbini: None. Background: The effectiveness of histopathological classification using CYP11B2 immunostaining in unilateral primary aldosteronism (PA) for predicting clinical and biochemical outcomes following adrenalectomy remains a topic of debate. To date, no studies have conclusively shown that HISTALDO influences hypertension remission, and its effect on biochemical success varies among different ethnic groups. Methods: We conducted a cohort study involving 131 consecutive patients with unilateral PA who underwent unilateral adrenalectomy. Aldosterone-producing adrenal lesions were classified according to the HISTALDO criteria. Biochemical and clinical outcomes were assessed using the PASO criteria. Results: Among the 131 adrenal lesions, classical and non-classical histology were identified in 101 (77.09%) and 30 (22.91%) cases, respectively. In the classical group, 89 cases were classified as aldosterone-producing adenoma (APA), and 12 as aldosterone-producing nodule (APN). Within the non-classical group, 27 cases (90%) had multiple aldosterone-producing micronodules (APM), and 3 cases (30%) had multiple APNs. Patients with classical histology were younger (p = 0.028) and predominantly female (p = 0.028) compared to those with non-classical histology. Classical histology was associated with higher rates of complete biochemical success (97.03% vs. 68.97%, p < 0.001) and complete hypertension remission (34.34% vs. 10.71%, p < 0.001) compared to non-classical histology. Although clinical and biochemical outcomes were similar between APA and APN, their immunohistological characteristics differed (fewer clear cells and stronger CYP11B2 staining in APN). In multivariable analysis, classical histology remained independently associated with complete biochemical (p < 0.001) and clinical (p = 0.037) success. Conclusion: Classical histology was an independent variable associated with more severe PA, complete biochemical and hypertension remission in surgically treated patients with unilateral PA. Moreover, the distinction between APA and APN did not differentiate outcome. Support: This work was supported by the Sao Paulo Research Foundation (FAPESP), process number 2019/15873-6 (to M.Q. Almeida), FAPESP fellowship 2021/09879-1 (to A.A.W.M.) and 2021/10101-5 (to A.G.G.). M.Q.A was also supported by National Council for Scientific and Technological Development (CNPq) 304091/2021-9. Presentation: Monday, July 14, 2025