Abernethy malformation is a rare congenital disorder characterized by abnormal development of the intrahepatic portal venous system, resulting in pathological shunting between the portal vein and systemic circulation (1). The estimated prevalence of this condition is approximately 1/50,000 to 1/30,000, making it an exceptionally uncommon disease (2). While frequently associated with various complications and congenital anomalies, renal involvement in this condition is exceptionally uncommon. We report the case of a 31-year-old male who presented with hematuria and proteinuria. During hospitalization, cirrhosis was identified. Renal biopsy confirmed Immunoglobulin A (IgA) nephropathy. Subsequent investigation of hepatic encephalopathy led to the definitive diagnosis of type II Abernethy malformation. Following surgical partial occlusion of the portosystemic shunt, the patient exhibited marked reduction in proteinuria.

A 30-year-old male was admitted on December 7, 2020, with worsening intermittent edema over 1 month following a year-long history of bilateral lower extremity edema initially noted in 2019. Hospitalization after outpatient investigations revealed significant hypoalbuminemia (serum albumin 19.3 g/L), proteinuria (2+), hematuria (3+), and 24 h urinary protein excretion of 1.18 g, leading to a provisional diagnosis of chronic glomerulonephritis with hypoalbuminemia. On admission, physical examination demonstrated mild pitting edema of the eyelids and lower extremities with unremarkable cardiopulmonary and abdominal findings. Laboratory studies confirmed proteinuria (2+) and hematuria with 64 dysmorphic RBCs/HPF, progressive hypoalbuminemia (albumin 16.0 g/L, total protein 42.3 g/L), elevated liver enzymes (AST 43 U/L), hypercholesterolemia (total cholesterol 5.93 mmol/L), markedly elevated CA-125 (142.00 U/mL) and ferritin (328.30 ng/mL), with immunology showing IgA elevation (591 mg/dL) and low C3 (53 mg/dL). Notable imaging included abdominal CT revealing cirrhosis with splenomegaly, ascites, and gastroesophageal varices, renal ultrasound demonstrating increased parenchymal echogenicity, and echocardiography diagnosing asymmetric non-obstructive hypertrophic cardiomyopathy. All other investigations—including comprehensive serological, immunological, viral, and metabolic panels—returned normal results, with no significant past medical or family history documented.

Renal biopsy performed on December 11, 2020, obtained 20 glomeruli. Light microscopy revealed three glomeruli with segmental sclerosis and capsular adhesions, one small cellular crescent, and one cellular crescent with segmental fibrinoid necrosis. The remaining glomeruli displayed mild mesangial hypercellularity and matrix expansion with focal endocapillary proliferation, alongside PAS-positive deposits in mesangial regions. Tubular findings featured vacuolar and granular degeneration with focal atrophy, while the interstitium demonstrated mild fibrosis with lymphomonocytic infiltration. Arterioles exhibited wall thickening and luminal narrowing. Immunofluorescence showed granular mesangial deposits positive for IgA (++), IgM (++), and C3 (+), with equivocal IgG (±) and negative C1q. Electron microscopy confirmed electron-dense deposits in mesangial and subendothelial zones with diffuse podocyte foot process effacement (Figure 1), establishing a diagnosis of mesangial proliferative IgA nephropathy (Lee Grade III, Oxford Classification M1E0S1T0-C1). Given negative HBV-DNA, the clinical diagnosis included IgA nephropathy, cirrhosis, and hypercholesterolemia. To mitigate bleeding risks from portal hypertension, therapy was initiated with low-dose methylprednisolone (16 mg/day), mycophenolate mofetil (0.5 g twice daily), and statin therapy. Suboptimal medication adherence led to self-guided dose reduction and treatment discontinuation, resulting in recurrent edema flares and repeat hospitalization. Proteinuria fluctuated between 0.8–2.1 g/day. Despite recommendations for angiographic evaluation and liver biopsy to determine the cause of liver dysfunction, the patient rejected invasive procedures and was managed with hepatoprotective agents. Changes in liver function parameters at baseline and during follow-up are summarized in Table 1.

During 2023, the patient required three hospital admissions for recurrent hepatic encephalopathy episodes. Angiography (April 2023) revealed a high-flow portocaval shunt draining into the inferior vena cava, accompanied by attenuated main portal vein branches, dilation of the superior mesenteric and splenic veins, high-risk gastroesophageal varices, and anomalous left subphrenic vessels anastomosing with the left renal vein (Figure 2). Multidisciplinary consensus confirmed type II Abernethy malformation. Preoperatively, an upper endoscopy was performed and revealed only chronic non-atrophic gastritis, without varices protruding into the lumen. In May 2023, laparoscopic partial occlusion of the portosystemic shunt was performed. The liver, inspected under laparoscopy, was small and nodular, consistent with the gross morphological diagnosis of cirrhosis. Intraoperative ultrasound confirmed the absence of focal hepatic lesions. Intraoperative exploration identified a 2.5-cm shunt vessel at the porta hepatis. Trial clamping induced marked gastrointestinal venous engorgement, prompting abandonment of complete ligation due to hemorrhage risk; consequently, 80% luminal reduction was achieved. Postoperatively, portal flow velocity increased to 10–12 cm/s (baseline: 6–8 cm/s) with progressive ammonia normalization. Notably, proteinuria decreased to 0.19–0.29 g/24 h at 2 months (pre-intervention range: 0.8–2.1 g/24 h), with urinalysis showing trace protein, 1 + hematuria, and 27.4 RBCs/HPF. Maintenance therapy with finerenone and beraprost sodium was continued. During 10-month follow-up, only one additional hepatic encephalopathy event occurred. Postoperative follow-up CT demonstrated no further progression of varices, with a marked reduction in ascites compared with preoperative findings. During subsequent follow-up, no episodes of gastrointestinal bleeding have been observed.

Abernethy malformation is a rare congenital anomaly involving portosystemic shunts. Based on the integrity of portal vein development, it was categorized anatomically as Type I (complete shunt with absent portal vein) or Type II (partial shunt with preserved portal venous system) (1, 3). This disorder affects many systems, often leading to complications including cirrhosis, hepatic encephalopathy, and cardiovascular abnormalities (4). Notably, involvement of the renal system is uncommon. There have been less than ten reports of Abernethy malformation with glomerulonephritis. The patterns of disease include MPGN, IgA nephropathy and membranous nephropathy (Table 2) (5–10).

This patient concurrently presented with type II Abernethy malformation and biopsy-proven IgA nephropathy, progressively developing liver dysfunction, hepatic encephalopathy, and hypertrophic cardiomyopathy during the disease course. The cardiomyopathy likely represents cardiac compensatory adaptation to chronic portosystemic shunting, while hepatic dysfunction stem from portal hypoperfusion-induced parenchymal extinction (1, 11). Notably, cirrhosis itself constitutes the most common etiology of secondary IgA nephropathy, primarily mediated through aberrant IgA1 glycosylation, impaired hepatic reticuloendothelial clearance, and defective immune complex removal (12–14). In our case, the absence of prior hepatitis, insidious progression to cirrhosis/encephalopathy, and renal histopathology demonstrating dominant mesangial IgA deposits with subendothelial extension are diagnostically aligned with cirrhosis-associated glomerulopathy (15).

Critically, Abernethy malformation may instigate IgA nephropathy through portosystemic shunting prior to liver dysfunction development, suggesting an independent pathogenic role of vascular diversion in the IgA nephropathy pathogenesis (16). As demonstrated by Karashima et al., shunt fractions exceeding 90% substantially elevate nephropathy risk—likely mediated by systemic spillover of IgA immune complexes circumventing hepatic reticuloendothelial filtration, thereby triggering immune-mediated glomerular injury (17). Although our patient exhibited radiologic features consistent with cirrhosis (CT-confirmed hepatic nodularity, splenomegaly, and varices) at IgA nephropathy diagnosis, the profound and sustained proteinuria reduction following partial portosystemic shunt occlusion (from preoperative fluctuations of 0.8–2.1 g/24 h to stable 0.19–0.29 g/24 h) compellingly implicates aberrant shunting as a pivotal driver of glomerulopathy. This observation aligns with Okamoto et al.’s report of nephrotic syndrome remission after shunt embolization without immunosuppression (18). Collectively, these findings indicate that correcting portosystemic shunts directly modulates renal disease activity, operating independently or synergistically with underlying hepatic pathology.

Furthermore, Dash et al. demonstrated that patients with non-cirrhotic portal fibrosis undergoing splenorenal shunt surgery exhibited increased IgA nephropathy incidence attributable to augmented portosystemic shunting with compromised hepatic clearance. In contrast, those with extrahepatic portal vein obstruction and preserved hepatic parenchymal function showed no post-procedural nephritis escalation (19). This implies that IgAN development is jointly governed by shunt magnitude and hepatic immunological clearance capacity (Figure 3), explaining both the absence of universal renal involvement in Abernethy malformation and the substantial age-of-onset heterogeneity.

According to presently evolved management paradigms, liver transplantation should be carried out in type I Abernethy malformation while shunt correction may be reserved for atypical type II patients symptomatic like hepatic encephalopathy patients (1). However, there is little information about the long-term benefits of portosystemic shunt treatment for kidney function. The reduction in protein and red blood cells in the urine following the procedure in our case adds evidence of a connection between these shunts and IgA nephropathy. This finding is consistent with the longitudinal study by Okamoto et al. which showed that embolization of aberrant shunts can improve nephrotic syndrome, renal function, and histological damage without immunosuppression therapy (18). Despite these encouraging signals, the strength of the claims about the long-lasting effects of shunt modification on IgA nephropathy must be shown in prospective trials.

Despite its rarity, Abernethy malformation necessitates multidisciplinary management due to its multisystem manifestations—particularly for monitoring long-term renal outcomes. The improvement in nephropathy symptoms following portosystemic shunt correction in this case suggests that early intervention may mitigate progressive glomerular injury. Future multi-center studies are warranted to establish the therapeutic efficacy of shunt modification on sustained renal function preservation.