Clinical Study of Eleven Patients with Midbrain Infarction-Induced Oculomotor Nerve Palsy

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Background

Midbrain lesion-induced oculomotor nerve palsy can be divided into the nuclear and infranuclear types. In the infranuclear type, the degree of each subtype of ocular muscle palsy usually varies.

Methods

The neuroradiological findings of 11 patients with midbrain infarction-induced oculomotor nerve palsy were analyzed. Their infarcts were grouped into rostral and caudal lesions. Each group was then divided into lesions that occurred in the paramedian and lateral regions before being subdivided further into lesions that occurred in the tegmental, central, and ventral areas.

Results

Unilateral and bilateral infarcts were seen in 9 and 2 patients, respectively. The ventrocentral area of the rostral paramedian region was the most commonly affected part. External ocular muscle palsy was observed in all 11 patients. Ten patients had infranuclear oculomotor nerve palsy. Of these 10 patients, 9 had adduction palsy. Internal ocular muscle palsy was detected in 4 patients. The patient with nuclear type had bilateral ptosis and bilateral elevation palsy and did not exhibit Bell's phenomenon; however, her lesion was unilateral. Vertical gaze palsy was detected in 3 patients who continued to exhibit Bell's phenomenon.

Conclusions

In the 3 cases in which patients with vertical gaze palsy continued to exhibit Bell's phenomenon, it was considered that the palsy was caused by impairment of the rostral interstitial nucleus of the medial longitudinal fasciculus. Our study suggested that the intra-axial fascicular fibers innervating the medial rectus muscle are particularly susceptible to infarction, possibly because they are the most centrally located in the intra-axial oculomotor fascicular fibers.

Section snippets

Characteristics of the Enrolled Patients

We studied the neurological and magnetic resonance imaging (MRI) findings of 11 patients with midbrain infarction-induced oculomotor nerve palsy caused by midbrain infarction (Table 1). The medical charts of our 2 university hospitals were retrospectively reviewed by 1 of the authors (K.O.), and 11 consecutive patients with oculomotor nerve palsy due to midbrain infarction were identified. Their ages ranged from 30 to 88 years old. Six patients were male and 5 patients were female. In the 11

Distribution of the Patients' Infarcts

The paramedian region was affected in all 11 patients, and the lateral area was also affected in 2 patients (patients 6 and 11) (Table 1, Table 2). The infarcts were located in the rostral paramedian region in 8 patients (patients 1-5, 8, 9, and 11), in the caudal paramedian region in 2 patients (patients 7 and 10), and in the rostral and caudal paramedian regions in 1 patient (patient 6). The bilateral paramedian regions were affected in 2 patients (patients 3 and 6). The infarcts extended to

Discussion

The oculomotor nerve nucleus is located in the centromedial part of the rostral midbrain (Fig 2).16 Both the oculomotor nerve nucleus and its intra-axial fascicular fibers are supplied by the superior medial mesencephalic branch (sMMB) (Fig 2).15 The sMMB consists of the inner sMMB and outer sMMB.15 The intra-axial oculomotor fascicular fibers are supplied by the inner sMMB from the medial side and by the outer sMMB from the lateral side (Fig 2).15 The sMMB also supplies the red nucleus and the

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