| OCR Text |
Show /. Clin. Neuro-ophthalmol. 1: 247-248, 1981. A special feature for this issue of the Journal is this highly magnified photograph of a mid-sagittal brain preparation. This will allow you to look directly into the third ventricle and to have a brief review of neuroanatomy in an area of particular interest to neuro-ophthalmologists. Emphasis is given here to the diencephalon. Recall that the diencephalon plus the telencephalon make up the cerebrum. The telencephalon is made up of the cerebral hemispheres and the diencephalon forms the central core. The diencephalon consists of four parts, divided into symmetrical halves by the third ventricle. Thus, the diencephalon is made up of the thalamus, subthalamus, epithalamus, and hypothalclmus. In this picture, if you draw a line passing just below the mammillary body ("MB") and passing through the posterior commissure ("p"), you will see the junction of midbrain ("M") below and diencephalon above. Likewise, if you draw a line from foramen of Monro ("FM") to optic chiasm ("C"), you will see the boundary between the diencephalon (caudal to this line) and the telencephalon (rostral to this line). Thin black lines have been drawn on this diagram to show a line from anterior margin of foramen Monro above to the posterior-superior midportion of the optic chiasm below (boundary of telencephalon-diencephalon) and again from caudal boundary of mammillary body to posterior commissure (boundary of diencephalon-mesencephalon) in this picture. The space of the slit-like third ventricle is the space you are looking into between these two lines. Thus, the anterior wall of the third ventricle is fonned by the lamina tenninalis (delineated by the white arrowhead). The lateral wall of the third ventricle is marked by the hypothalamic sulcus (shown by "H") in this picture. Above this shallow groove is the thalamus and below this "H" is the hypothalamus. The floor of the third ventricle is actually indented by the optic chiasm. The triangular space above the chiasm (but still in the third ventricle) is called the optic recess, and this area is particularly important to delineate when pneumoencephalograms are done to look for chiasmal tumors. Behind the chiasm is a shallower infundibular recess, not as well seen in this partic- September 1981 Neuro-anatomical Feature Photo J. LAWTON SMITH, MD. ular specimen. Behind the chiasm is the median eminence and then the tuber cinereum ("tc"). A black arrowhead points to the opening of the cerebral aqueduct in this specimen. A notch in the posterior margin shows the pineal recess. The roof of the third ventricle is attached along the striae medulla res thalami, and a small choroid plexus is suspended from the roof. In this picture, "cp" shows some of the choroid plexus. The anterior commissure ("ac") is seen anterior to the fornix ("F") which fonns the anterior boundary of foramen Monro. The great white commissure- corpus callosum ("CC")-connecting the two hemispheres is seen above with the genu ("g") at anterior (rostral) margin and the splenium at the posterior margin ("s"). Septum pellucidum has been dissected away and one is then looking into the opposite lateral ventricle ("LV"). The quadrigeminal plate on posterior aspect of mesencephalon is shown with "SC" representing the superior colliculus and "IC" the inferior collicus. Midbrain (mesencephalon) is "M" and rostral portion of the pons ("P") is just seen at lower margin of the picture. The medial aspect of hypothalamus is divided into three regions-suprachiasmatic, tubera!, and mammillary-using the chiasm, tuber cinereum, and mammillary bodies as ventral structures to delineate these regions. No massa intermedia (interthalamic adhesion) is seen in this specimen (connecting the thalamus from one side to another) and this structure is missing in about 30% of brain specimens. It is hoped that this picture will help refresh the ophthalmologist regarding the integral relationships of the chiasm to the structures of the brain and diencephalon. Readers are encouraged to submit high-quality black and white photographs of various tissue specimens, or other pictures-as good external or fundus photographs- to be considered for feature photos in subsequent issues of the Journal of Clinical Neuroophthalmology. I'd like to thank Dr. Ronald G. Clark for allowing me access to this specimen so that I could take the picture, too. Write for reprints to: J. lawton Smith, M.D., 9820 S.W. 62nd Court, Miami, Florida 33156. 247 Neuro-anatomical feature photo (J () en 24t\ Journal of Clinical Neuro-ophthalmollilll |
