Injury of the thalamocingulate tract in the Papez circuit by ventriculoperitoneal shunt: A case report

Systemic Review: Neurological Deficits following Ventriculoperitoneal Shunt (VPS) Insertion

A reduction in fluid absorption or an obstruction of normal outflow is a common cause of hydrocephalus. It typically requires medical attention, which frequently entails the placement of a ventriculoperitoneal shunt (VPS) to lower intracranial pressure. We intend to list the few, documented examples of neurological impairments resulting from the installation of a VPS in this systematic study. Two search engines (PubMed and Cochrane) were used to conduct a systematic review from 1975 to December 12, 2021. The following search terms were employed: neurological deficits or neurological injury or palsies or thalamus or tract or longitudinal fasciculus or somatotropy or fasciculus or hearing loss or hemisensory or cortico AND ventriculoperitoneal shunt or VPS AND hydrocephalus. The inclusion criteria included VPS, neurological deficits, and human participants. The exclusion criteria included ventriculoarterial shunt, lumboperitoneal shunt, nonhuman subjects, and infection. Twenty trials in total, including a total of 25 patients, were included. There were 17 case report studies. A total of 35/785 patients (4.46%) experienced neurological impairments. In 9/25 (36%) of shunt cases had one of the three recognized causes: trapped fourth ventricle, dandy walker, or syringomyelia. Most of the patients developed VI, VII nerve palsies 11/25 (44%) followed by weakness, cerebellar symptoms, and VI nerve palsy. The brainstem was seen to be the most often injured structure (15/25; 60%), followed by deep brain structures (thalamus, basal ganglia, and white matter tracts; 20%). Even though ventriculoperitoneal shunting is a routine and straightforward treatment, issues can still arise. Although rare, there have been reports of cranial nerve impairments, therefore care should be taken.

Papez's Forgotten Tract: 80 Years of Unreconciled Findings Concerning the Thalamocingulate Tract

The thalamocingulate tract is a key component of the Papez circuit that connects the anterior thalamic nucleus (ATN) to the cingulum bundle. While the other white matter connections, consisting of the fornix, cingulum bundle and mammillothalamic tract, were well defined in Papez's original 1937 paper, the anatomy of the thalamocingulate pathway was mentioned only in passing. Subsequent research has been unable to clarify the precise anatomical trajectory of this tract. In particular, the site of thalamocingulate tract interactions with the cingulum bundle have been inconsistently reported. This review aims to synthesize research on this least studied component of the Papez circuit. A systemic approach to reviewing historical anatomical dissection and neuronal tracing studies as well as contemporary diffusion magnetic resonance imaging studies of the thalamocingulate tract was undertaken across species. We found that although inconsistent, prior research broadly encompasses two differing descriptions of how the ATN interfaces with the cingulum after passing laterally through the anterior limb of the internal capsule. The first group of studies show that the pathway turns medially and rostrally and passes to the anterior cingulate region (Brodmann areas 24, 33, and 32) only. A second group suggests that the thalamocingulate tract interfaces with both the anterior and posterior cingulate (Brodmann areas 23 and 31) and retrosplenial region (Brodmann area 29). We discuss potential reasons for these discrepancies such as altering methodologies and species differences. We also discuss how these inconsistencies may be resolved in further research with refinements of terminology for the cingulate cortex and the thalamocingulate tract. Understanding the precise anatomical course of the last remaining unresolved final white matter tract in the Papez circuit may facilitate accurate investigation of the role of the complete Papez circuit in emotion and memory.