The Anatomy of the Posterior Commissure.

AIM: The connections of posterior commissure are defined. Its fibers mediate the consensual light reflex by interconnecting the pretectal nuclei. The fiber connections from the thalamic, pretectal, superior colliculus and the habenular nuclei are known, but they have not been shown anatomically. The present study is a fiber dissection study to define the anatomy of the posterior commissure. MATERIAL AND METHODS: Twenty formalin-fixed sheep heads were used in the study. The specimens were fixed in 10% formalin solution for 3 weeks. The arachnoidal and vascular structures were removed by using a surgical microscope magnification (x6-x40) and brains were again fixed for 4 weeks at -20°C. The fiber dissections were performed at Marmara University, Rhoton Laboratory. Also, a radiological tractographic study was carried on five healthy volunteers to see the posterior commissure cortical connections. RESULTS: In fifteen sheep brains, the dimensions of the posterior commissure were measured as 1.36 mm (range 0.5-2.5 mm) width, and as 4.6 mm (range 3-6 mm) length. In the dissection study, a frontotemporooccipital fascicle was observed to connect with the fibers of the posterior commissure. Diffusion tensor imaging scans showed the frontotemporooccipital tract to extend to posterior commissural region. CONCLUSION: To our knowledge, this is the first anatomical and tractographic study regarding the posterior commissure. However, further human cadaveric studies are necessary.

The Probst bundle associated with anomalies of the precommissural separated fornix in an acallosal brain

Dissection of the brain disclosed a unique form of the Probst bundle and a rare variation of the precommissural fornix. The latter showed an unusual size, branches and path on the medial surface of hemisphere. Its posterior branch continued to curve parallel with the posterior commissural fornix to follow an abnormal path and end in the hypothalamus. The Probst bundle was intermingled with the separated fornix in an anteroposterior direction as well as in the anterior and posterior parts in an atypical way. Focusing on such morphological abnormalities may help to gain a better understanding of the pathophysiology of brain disorders (AU)

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