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The circumventricular organs are highly specialised sites in the brain. They lie outside of the blood–brain barrier, are located periventricularly, and are thought to play an important role as the gateway through which information reciprocates between the outside and inside of the brain.1 We have attempted to visualise the circumventricular organs with the use of a fluorescence endoscope at the time of ventriculoperitoneal shunt revision.
A 71 year old man presented with progressive decline in mental acuity and gait disturbance. A ventriculoperitoneal shunt had been placed for normal pressure hydrocephalus following cerebral contusion 20 years before. The shunt was found to be obstructed, and was replaced with a pressure programmable valve during ventriculoperitoneal shunt revision surgery. The existing ventricular catheter was extracted from the left lateral ventricle after we confirmed that there was no adhesion to the choroid plexus with the fiberscope inserted into the right lateral ventricle by observing through the defect in the septum pellucidum. We used the fiberscope, measuring 5 mm in diameter, to inspect the interior of the lateral and third ventricles in white light mode (fig 1A). The fiberscope is equipped with dual observation modes for both white light and fluorescence. It was originally developed for photodynamic diagnosis of epithelial dysplasia of the bronchus under excitation with blue light (D-Light AF system; Karl Storz Endoscopy).2 A solution of 500 mg of fluorescein sodium was administered intravenously to the patient while the interior of the ventricle was observed with the fiberscope in fluorescence mode. About 20 seconds after the injection, the choroid plexus began to glow yellow–green under the effect of the fluorescein (fig 1B). In the third ventricle the median eminence on the floor and the organum vasculosum of the lamina terminalis also became visible, glowing with yellow–green fluorescence (fig 2).
Fluorescein sodium is commonly used in fluorescein angiography for diabetic retinopathy. The retinal lesions characterised by the damaged blood–retinal barrier can be diagnosed by leakage of the dye.3 This same effect can occur in the brain; in most parts of the brain the dye can not pass across the capillary walls because of the blood–brain barrier. However, several locations in the brain without the blood–brain barrier, such as the circumventricular organs and the choroid plexus, allow the dye to permeate and become visible by fluorescence. Although we could not confirm this phenomenon in the circumventricular organs other than at the median eminence and the organum vasculosm because of limited accessibility with the fiberscope, we think this method of observation may contribute to a better understanding of the circumventricular organs in living humans.
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