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NIdiopathic normal pressure hydrocephalus (iNPH) is a heterogeneous and under-characterized syndrome, especially from a neuropsychological perspective. We present the case of M.L., a 50-year-old man who was found to have marked quadriventricular enlargement (Evans index = 0.45), incidentally identified following a transient episode of jargon aphasia. Despite the absence of gait disturbance, urinary symptoms, or functional impairment, neuropsychological evaluation revealed a mild, isolated dysexecutive syndrome affecting auditory–verbal working memory and reactive mental flexibility. Global cognition, episodic memory, processing speed, and visuoconstructive abilities were preserved. This pattern is consistent with a subtle fronto-subcortical dysfunction and raises questions about the causal relationship between ventricular dilation and executive deficits, particularly in light of potential confounding factors, including chronic alcohol use and untreated mild sleep apnea. From a clinical perspective, this case exemplifies the diagnostic challenges posed by “compensated” iNPH, in which severe ventriculomegaly may be present despite minimal or absent clinical manifestations. From a theoretical perspective, the preservation of cognitive efficiency despite significant cerebral volume reduction supports a connectionist view of brain organization and highlights the role of neuroplastic mechanisms in functional compensation. This report underscores the importance of systematic and detailed neuropsychological assessment in suspected or incidental iNPH, as brief cognitive screenings (e.g., MMSE) may fail to detect subtle executive dysfunctions. Longitudinal cognitive monitoring is warranted to clarify the clinical trajectory and potential transition toward neurodegenerative processes. By documenting this rare asymptomatic iNPH case, the study contributes to refining the neuropsychological phenotype of the disorder and highlights the critical need to integrate cognitive evaluation into diagnostic and follow-up protocols for iNPH.