Introduction:

Recent functional data support a major role of the precuneus in higher order functions. Nevertheless, until date the fiber tracts implicated in its connectivity have not been adequately investigated. To that end fiber-microdissection studies were complemented with DTI protocols to study its connectivity. Interestingly, a previously unrecognized, fiber tract was consistently identified during the microdissection process thus prompting further focused investigation of its structure, morphology and architecture.

Methods:

Nine (9) normal, adult, cerebral cadaveric hemispheres were processed with the Klingler’s method and were studied through the fiber microdissection technique. Additionally, a tailored DTI protocol was utilized including a region-of-interest (ROI) approach based on anatomical landmarks derived from preliminary results of the fiber microdissection studies.

Results:

This tract was consistently identified as a distinct group of fibers residing at the depth of the anterior bank of the parieto-occipital sulcus, distal calcarine fissure and medial temporal lobe, exhibiting an oblique dorso-ventral trajectory. Running from the posterior precuneus to the temporal pole, this tract follows the direction of the parieto-occipital sulcus, and passing through the retrosplenial area it reaches the parahippocampal place area where it widens, curves laterally and projects towards the temporal horn to finally reach the temporal pole. White matter fiber microdissection and tractographic findings showed correspondence regarding the tract’s topography, morphology and connectivity. We named this newly recognized tract the “Retrosplenial Aslant Tract” (RAT) due to its architectural silhouette and spatial fiber density pattern.

Conclusions:

This study provides original anatomo-imaging evidence of a newly identified, fiber pathway named the “Retrosplenial Aslant Tract”. This white matter pathway connects precuneal and temporal areas through the retrosplenial subcortical corridor. Our results indicate that the RAT is responsible for the connectivity of areas functionally implicated in high order functions such as memory, consciousness, spatial updating, navigation, and visuomotor planning. Future studies are needed to elucidate its' functional significance.

Patient Care:

Solid understanding of the human brain's internal architecture is necessary for neurosurgeons caring for patients with intraparenchymal lesions. Surgical corridors involving eloquent regions should be preoperatively recognized and avoided to prevent neuropsychological morbidity. Better understanding of the brain’s structure to function relationship has led to the wide propagation of awake cortical and subcortical mapping into routine neurosurgical practice aiming to achieve the patient’s optimal onco-functional balance. However, certain tracts and their respective functions are difficult to map. Thus, preoperative information regarding transecting fibers can prove pivotal. Furthermore, the new concept of brain hodotopy places the integrity of white matter fiber tract anatomy in a central role for cerebral physiology and function. In this context, original evidence regarding cerebral fiber tract architecture not only refines neuroanatomical knowledge but also provides valuable insight into the brain’s axonal connectivity and organization.

Learning Objectives:

To introduce a previously unrecognized fiber tract and to enhance neuroanatomical knowledge regarding the connectivity of the precuneus and temporal lobe.

References:

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