The course of facial corticobulbar tract fibers in the dorsolateral medulla oblongata

Abstract

Background The course of the corticobulbar tract (CBT) to the facial nucleus has been investigated by some previous studies. However, there are some unclear points of the course of the CBT to the facial nucleus. This study aimed to elucidate the detailed course of the CBT to the facial nucleus through the analysis of lateral medullary infarction (LMI) cases. Methods The neurological characteristics and magnetic resonance imaging findings of 33 consecutive patients with LMI were evaluated. The location of the lesions was classified rostro-caudally (upper, middle, or lower) and horizontally. Further, we compared the neurological characteristics between the groups with and without central facial paresis (FP). Results Eight (24%) patients with central FP ipsilateral to the lesion were identified. Dysphagia and hiccups were more frequently observed in the group with central FP than in the group without central FP. In patients with central FP, middle medullary lesions and those including the ventral part of the dorsolateral medulla were more frequently observed. Contrastingly, patients with lesions restricted to the lateral and dorsal regions of the dorsolateral medulla did not present with central FP. Conclusion The results of this study indicate that the CBT to the facial nucleus descends with the corticospinal tract at least to the middle portion of the medulla, and then ascends to the facial nucleus through the medial and ventral areas of the dorsolateral medulla after decussation.

Topographic Consideration on the Occurrence of Ipsilesional Facial Paresis in Lateral Medullary Infarction

“…When it comes to the other manifestations, all the clinical features statistically related to FPdysphagia, dysarthria, and hiccupsare attributed to the damage of the nucleus ambiguus, and the nucleus is located in relatively ventral region among the dorsolateral medulla. Kanbayashi et al suggested corticobulbar fibers would ascend to the facial nucleus through the medial and ventral areas of the dorsolateral medulla after decussation [10], and clinical finding in the present study is supporting this idea. Including typical = "typical" + "typical and dorsal" + "typical and lateral" + "large"; including ventral = "ventral" + "large"; including dorsal = "dorsal" + "typical and dorsal" + "large"; including lateral; "lateral" + "typical and lateral" + "large."…”

“…In this study, all the studied patients with FP showed central-type FP, ipsilateral to infarct lesion, and the lesions were mostly located in the upper medulla. A recent study dealing with the similar topic said that the corticobulbar fiber would at least descend to the portion of the middle medulla [10], but in the present study, patients with lesions restricted to the middle medulla rarely showed FP. This finding suggests that the aberrant corticobulbar fiber innervating the contralateral lower face decussates and takes ascending course at the upper medulla [5,9].…”

“…The most feasible hypothesis was referred to "aberrant looping fiber." It has been suggested that corticobulbar fiber innervating the lower face runs down to the level of the medulla and then takes aberrant course looping to the contralateral facial nucleus across the dorsolateral medulla [3,[8][9][10].…”

“…However, central-type FP has been occasionally reported as a manifestation of lateral and medial medullary infarction (MMI) [1][2][3][4][5][6][7][8]. To explain this phenomenon, it has been suggested that CBT fibers for the lower face descend to the level of the medulla and then decussate to the opposite side [8][9][10]. There have been a few observational studies with small sample size, trying to verify such anatomical hypothesis [9,10], but none of the studies considered possible confounding factors such as age, etiology, or comorbidity.…”

“…To explain this phenomenon, it has been suggested that CBT fibers for the lower face descend to the level of the medulla and then decussate to the opposite side [8][9][10]. There have been a few observational studies with small sample size, trying to verify such anatomical hypothesis [9,10], but none of the studies considered possible confounding factors such as age, etiology, or comorbidity. This study was performed to investigate the relationship between the location of infarct lesion and the occurrence of FP in lateral medullary infarction (LMI), as well as to explore any related clinical features or risk factors.…”