Anatomical study of the arachnoid envelope over the pineal region.

Background: The distribution of the arachnoid membrane and its relationship with the neurovascular structures in the pineal region are still not fully understood.

Objective: Because the arachnoid membrane has an intimate relationship with the neurovascular structures in the pineal region and it will always be encountered surgically, we attempted to clarify the formation and distribution of the arachnoid envelope over the pineal region (AEPG).

Methods: The formation and distribution of the AEPG and its relationship with the neurovascular structures in the pineal region were examined by anatomic dissection in 20 adult cadaveric formalin-fixed heads.

Results: The supratentorial and infratentorial outer arachnoid membranes converged at the tentorial apex and then embraced and ran forward along the vein of Galen to form the AEPG. The AEPG could be divided into 2 parts. Typically, the posterior part of the AEPG enveloped the vein of Galen and the terminal segments of its tributaries, and the anterior part of the AEPG enveloped the suprapineal recess, the pineal gland, and the distal segment of the internal cerebral veins. The compartment demarcated by the AEPG did not communicate with the adjacent subarachnoid cisterns or space.

Conclusion: Previous knowledge about the AEPG, as well as the superior boundary and the contents of the quadrigeminal cistern, needs to be revised. The arrangement and individual variation of AEPG are important for a better understanding of the various growth patterns of the pineal tumors and the relationship between the tumor and the neurovascular structures in the pineal region.