Polyuria, or excessive fluid loss through the kidneys, is a common issue in neurocritical patients, often resulting from conditions such as fluid volume overload, osmotic diuretics, central diabetes insipidus (CDI), or cerebral salt wasting syndrome (CSWS). Notably, the specific cause of postoperative polyuria within 24 h in patients with tumors located in the supratentorial non-midline region remains poorly understood. To address this gap, we conducted a prospective observational study with 30 patients and found that eight (26.7%) experienced postoperative polyuria. Binary logistic regression analysis of clinical data ruled out fluid volume and osmotic diuretics as the underlying causes of postoperative polyuria, and suggested a very subtle association between tumor size and polyuria (OR = 1.030
p = 0.041). A significant postoperative decrease in serum sodium levels in the polyuria group (p = 0.005) pointed towards CSWS as potential mechanism. Differentiating between CDI and CSWS, both involving neuroendocrine hormone dysregulation, is challenging due to the lack of efficient clinical tests. To overcome this, we developed a novel liquid chromatography-tandem mass spectrometry (LC-MS)-based targeted and quantitative method to measure seven neuroendocrine hormones, including antidiuretic hormone (ADH) related to CDI and six natriuretic peptides associated with CSWS. Elevated levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and ADH were observed in the polyuria group. Univariate analysis identified ANP, BNP, and ADH as significantly associated with polyuria at a threshold of p <
0.1. Later, multivariate logistic regression further revealed elevated BNP as an independent risk factor for polyuria (OR = 9111.901
p = 0.022). These findings suggest that CSWS may be the primary cause of postoperative polyuria in patients with supratentorial non-midline tumors, as evidenced by the concomitant decrease in serum sodium and increase in natriuretic peptides, particularly BNP.