The subcommissural organ (SCO) is a small ependymal gland located in the posterior part of the third ventricle, beneath the posterior commissure [2][4]. It secretes glycoproteins into the cerebrospinal fluid that aggregate to form Reissner’s fiber, which descends through the aqueduct and central canal [1][3]. The SCO is innervated by serotonergic and noradrenergic fibers from the dorsal and median raphe nuclei, locus coeruleus, and nucleus of the solitary tract [2][5]. These modulate SCO secretory activity, with serotonin and norepinephrine having stimulatory effects [3][6]. The SCO is also regulated by pituitary hormones as well as factors in the cerebrospinal fluid [1][4]. It plays a role in central nervous system development and regulation of cerebrospinal fluid composition [3][5]. Dysfunction of the SCO can alter ventricular flow dynamics and contribute to hydrocephalus [4][6].