MON-290 - Diagnostic Subtyping Strategies in Primary Hyperaldosteronism: Impact on HISTALDO Outcomes in 464 Adrenalectomy Cases

Background: Adrenal vein sampling (AVS) and cross-sectional imaging (CSI) are key for lateralizing primary hyperaldosteronism (PA), but their role in guiding adrenalectomy remains debated, especially with expanding indications for surgery. Furthermore, AVS is invasive, technically challenging, and available at few centers, resulting in most patients receiving lifelong escalating pharmacotherapy rather than curative surgery. This study evaluates histopathological outcomes using the HISTALDO classification across diagnostic subtyping strategies for unilateral and partial bilateral adrenalectomy (UA and pBA) in PA.

Methods: Between 01/01/2022-12/31/2025 (48 months), 1,965 consecutive adrenalectomies were performed at the Carling Adrenal Center (CAC); 464 cases on 461 patients (58.1% from outside of Florida) were for biochemically unequivocal PA (concomitant adrenal hypercortisolism in 14.3% of cases). The surgical and subtyping strategies varied and were A) UA for unilateral PA based on concordant AVS and CSI (n=16), B) UA based on AVS alone (negative CSI; n=25), C) UA after failed AVS based on CSI alone (n=10), D) UA after CSI alone (n=370), E) UA for bilateral PA and non-lateralizing AVS (n=34), and F) staged pBA (n=6). Overall, AVS was performed in 85 patients at 45 institutions. The mini back scope adrenalectomy was used in all cases. HISTALDO classification using CYP11B2 immunostaining defined lesions as aldosterone-producing adenoma (APA) or nodule (APN), multiple APN (MAPN/M), and diffuse hyperplasia (APDH).

Results: All patients were discharged within 23 hours of adrenalectomy. HISTALDO distribution varied significantly by group (p < 0.05). Classical pathology (APA/APN) predominated in concordant AVS-CSI (group A; 11/16: 69%) and UA after failed AVS based on CSI alone (group C; 7/10; 70%), while non-classical pathology (MAPN/M and APDH) was more common in group B (AVS-alone; 15/25; 60%), and D (CSI alone; 208/370; 56%), and groups E and F (30/34; 88%, and 6/6; 100%, respectively). Importantly, there was no difference in HISTALDO outcome for those with AVS (+/- CSI) versus CSI alone. Overall, AVS success rate (defined as accurate bilateral sampling and selectivity index >2) was 38 of 38 (100%) at CAC, compared to 37 out of 47 (79 %) at outside institutions.

Conclusion: The surgical and subtyping strategies used in PA are associated with HISTALDO pathology outcomes, which improve prognostication. However, the use of AVS did not increase the proportion of classical pathology (APA/APN). AVS at outside institutions was frequently not available, and when performed, failed in 21% of cases. AVS retains its greatest value for patients with CSI-negative PA who would otherwise be denied potentially curative adrenalectomy. Further studies are needed regarding the use of selective, severity‑ and imaging‑guided use of AVS in PA.