Oculomotor brainstem anatomy: nuclei to fascicles

Abstract

Over the last century there have been many advances in neuro-ophthalmology. Modern techniques of neuronal labeling have refined knowledge of the anatomy of the oculomotor nucleus and subnuclei that was originally based on anatomic studies. Non-invasive imaging of patients presenting with partial third nerve palsies has even more recently spawned theories of the arrangement of the axons of the oculomotor nuclei within the brainstem (the so-called fascicles). We present herein a discussion of the evolution of theories about the oculomotor subnuclear arrangements with a discussion of the more recent theories of fascicular organization.The early history of the study of the oculomotor nucleus is chronicled in the seminal 1953 monograph by Warwick [1] wherein he not only recounts the history of the study of the oculomotor nerve nucleus but also presents his own model. According to Warwick, interest in the organization of the oculomotor nerve nucleus dates back to the mid-nineteenth century when it was first defined by Stilling in 1846 [1]. Subsequently, various subnuclei were defined by those whose eponyms they bear (Edinger, Westphal, Perlia). The initial theories of oculomotor subnuclear organization were based on clinico-pathological studies, noting the condition of a patient in the pre-morbid state and examining the brain at autopsy to determine the location of the lesions [1]. In 1892, Nissl defined the changes seen in neuronal cell bodies with disruption of their axons. This discovery of chromatolysis made possible models based on pathologic examination of the midbrain after selective denervation of the extraocular muscles. In particular, the theory of Bernheimer (1897) Like Warwick some fifty years later, Bernheimer selectively extirpated extraocular muscles of monkeys and then sacrificed the animal ten days later and studied stained sections of the midbrain [2]. From the pattern of chromatolysis, Bernheimer derived his model of the oculomotor subnuclei. Bernheimer's model is somewhat difficult to understand since the two schemata presented differ in the orientation of the subnuclei. Warwick's depiction of Bernheimer's model shows oculomotor subnuclei stacked like pancakes rostral-caudally (Fig. 1) and, indeed, Bernheimer's drawing of a frontal slice through the oculomotor nucleus suggests such a picture (Fig. 2). However, Bernheimer has another sagittal view that is oriented dorsoventrally suggesting that the subnuclei form columns (Fig. 3). In either case, Bernheimer's model is interesting in that it places the subnuclei to the levator palpebrae muscle and superior rectus muscle in close proximity and, presumably, rostro-ventrally with ipsilateral innervation. It suggests bilateral innervation of the medial recti and inferior oblique muscles, the subnuclei of which lie behind and possibly below those of the superior rectus and levator palpebrae. The subnucleus to the inferior rectus is closest to the trochlear nucleus and provides contralateralinnervation. Finally, the subnucleus supplying the 'intrinsic' mu...

A Comprehensive Review on the Management of III Nerve Palsy

“…3,4 The central caudal nucleus (unpaired) in the midline innervates both the right and left levator palpebrae muscles. Thus lesion at this level results in bilateral ptosis.…”

Third Nerve Palsies

“…Other partial fascicular palsies have helped to clarify the topography of the fascicles within the midbrain. [1][2][3]8,67,68 The causes of fascicular oculomotor nerve lesions are nearly identical to those of lesions of the nuclear complex, with vascular causes heading the list, followed by infiltrative and inflammatory causes (Fig. 3).…”

“…83,85,[87][88][89]158,159 A large number of cases are recorded as "undetermined" cause and a larger proportion still, those of presumed ischemic origin, remain of uncertain location. Newer, more sensitive neuroimaging modalities, such as MRI, are localizing more of these lesions and even providing clues about pathogenesis, [1][2][3]8,[61][62][63][65][66][67][68] but most third-nerve palsies remain poorly characterized. Ischemic lesions causing oculomotor nerve palsies were believed to occur most frequently along the nerve's subarachnoid or intracavernous course, 95,135 although fascicular involvement was later demonstrated in some cases.…”

“…1-5). [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The oculomotor nerve (third cranial nerve) supplies motor innervation for the superior rectus, medial rectus, inferior rectus, inferior oblique, and levator palpebrae superioris muscles and also parasympathetic input to the pupillary constrictor and ciliary muscles. Cell bodies reside in the midbrain in a nuclear mass straddling the vertical midline (Figs.…”

“…1 and 2). [4][5][6][7][8] Each target muscle has a subnucleus devoted exclusively to its function (the medial rectus has three subnuclei 5 ). Most rostral and dorsal are the visceral nuclei (Edinger-Westphal nuclei and adjacent structures) that supply parasympathetic innervation to the pupillary sphincters and ciliary muscles via the ciliary ganglia.…”