Analysis of the anatomy of the Papez circuit and adjoining limbic system by fiber dissection techniques.

Fiber dissection techniques were used to study the limbic system, in particular the Papez circuit. The course, length and anatomical relations of the structures that make up the Papez circuit were delineated. Ten previously frozen and formalin-fixed cadaveric human brains were used, and dissected according to the fiber dissection techniques of Klingler et al. (Schweiz Arch Neurol Psychiatry 1935;36:247-56). The primary dissection tools were thin and curved wooden and metallic spatulas with tips of varying sizes. We found that the Papez circuit (mean length: 350 mm) begins in the hippocampus and continues into the fornix to reach the mamillary body. From there, the mamillothalamic tract continues to the anterior nucleus of the thalamus, which in turn connects to the cingulum by means of anterior thalamic radiations (mean length: 30 mm). The cingulum courses around the corpus callosum to end in the entorhinal cortex, which then projects to the hippocampus, thus completing the circuit. The average length and breadth of the mamillothalamic tract was 18 mm and 1.73 mm respectively. The average length of the cingulum was 19.6 cm and that of the fornix was 71 mm. The entire circuit was anatomically dissected first in situ in the hemisphere and was then reconstructed outside after removing its various components using fine fiber dissection under a surgical microscope. We found that fiber dissection elegantly delineates the anatomical subtleties of the Papez circuit and provides a three-dimensional perspective of the limbic system. Intricate knowledge of the anatomy of this part of the brain aids the neurosurgeon while performing epilepsy surgery and while approaching intrinsic brain parenchymal, ventricular and paraventricular lesions.