The volume, composition, and movement of the cerebrospinal fluid (CSF) are important for brain physiology, pathology, and diagnostics. Nevertheless, few studies have focused on the main structure that produces CSF, the choroid plexus (CP). Due to the presence of monocarboxylate transporters (MCTs) in the CP, changes in blood and brain lactate levels are reflected in the CSF. A lactate receptor, the hydroxycarboxylic acid receptor 1 (HCA1), is present in the brain, but whether it is located in the CP or in other periventricular structures has not been studied. Here, we investigated the distribution of HCA1 in the cerebral ventricular system using monomeric red fluorescent protein (mRFP)-HCA1 reporter mice. The reporter signal was only detected in the dorsal part of the third ventricle, where strong mRFP-HCA1 labeling was present in cells of the CP, the tela choroidea, and the neuroepithelial ventricular lining. Co-labeling experiments identified these cells as fibroblasts (in the CP, the tela choroidea, and the ventricle lining) and ependymal cells (in the tela choroidea and the ventricle lining). Our data suggest that the HCA1-containing fibroblasts and ependymal cells have the ability to respond to alterations in CSF lactate in body–brain signaling, but also as a sign of neuropathology (e.g., stroke and Alzheimer’s disease biomarker).

Undiagnosed significant hydrocephalus is an uncommon finding at forensic autopsy as many cases present in life with complex neurological symptoms. We present a case of a 46-year-old man with no neurological deficits or history of head trauma that was incidentally found to have a massive hydrocephalus at autopsy. This was found to be associated with an unruptured arteriovenous malformation completely confined to the choroid plexus as well as complete agenesis of the corpus callosum. The arteriovenous malformation was found to form a calcified obstruction at the foramen of Monro analogous to a mass lesion, such as a colloid cyst of the third ventricle. The association of this malformation and agenesis of the corpus callosum has never been described. Histologic examination of the brain confirmed significant loss of white matter tracts and thinning of the cortical ribbon due to pressure atrophy of the ependymal lining without significant gliosis, cortical dysplasia, or evidence of other developmental malformations. Autopsy is a vital tool in the evaluation of such rare cases, enhances epidemiologic data, and increases the understanding of these pathophysiological associations.