Neuroimaging of isolated and non-isolated third nerve palsies

Abstract

ABSTRACT. A variety of aetiologies may cause third nerve palsy (TNP), and some manifestations may herald neurological emergencies. This article describes and illustrates various diseases that lead to TNP. The two major functions of the third nerve are oculomotor and pupillomotor. The evaluation of patients with third nerve palsy (TNP) requires an understanding of the normal anatomy of the third nerve. The primary imaging modality used for patients with TNP is MRI because of its high soft-tissue contrast and ability to show the entire course of the third nerve. The MRI sequences used, besides T 1 weighted and T 2 weighted images, should include diffusion-weighted images, MR angiography, thin-slice (,1mm) steady-state free precession (SSFP) and contrast-enhanced spoiled gradientrecalled echo (SGRE) sequences. The current SSFP [e.g. fast imaging employing steady-state acquisition (FIESTA) for a GE scanner; constructive interference steady state (CISS) for a Siemens scanner] and SGRE sequences [e.g. spoiled gradient recalled (SPGR) for a GE scanner; fast low-angle shot (FLASH) for a Siemens scanner] provide submillimetric spatial resolution and are capable of depicting the cisternal segments of all 12 cranial nerves and the relationship of the nerves to pathological processes. They also allow reconstruction in multiplanar images that highlight the course of each cranial nerve (Figure 1). CT scanning is limited in patients with spontaneous subarachnoid haemorrhage (SAH) to exclude cerebral aneurysm and in patients head trauma with suspected skull fracture. Digital subtraction angiography is reserved for cases in which cerebral aneurysm or carotid-cavernous sinus fistula (CCF) is suspected and there is no clue on CT angiography or MR angiography. In this article, we discuss the anatomy and lesions in the

Acute Lymphoblastic Leukemia masquerading as surgical third nerve palsy: a case report

“…Furthermore, a more superior imaging modality would be magnetic resonance imaging as it gives high soft-tissue contrast and ability to show the entire course of the third nerve. CT scanning is limited in patients with spontaneous subarachnoid haemorrhage, or tumours [6].…”

Mesencephalon; Midbrain

“…Nuclear lesions usually occur due to small regions of infarction, and often there are no other neurological symptoms. In ventral midbrain, lesions are due to HYPERLINK "https://radiopaedia.org/articles/benedikt-syndrome" Benedikt syndrome and HYPERLINK "https:// radiopaedia.org/articles/weber-syndrome" Weber syndrome [2,5,19,20].…”

“…The fibers pass downward to lie inferiorly in the inferior division of the third nerve as it enters the orbit. These fibers synapse in the ciliary ganglion and give rise to postganglionic parasympathetic myelinated short ciliary nerves [1,19,20,21].…”

“…The accommodation reflex has its afferent input from the primary visual pathway; sequentially retina, optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation, visual cortex and area 17. The peristriate area 19 interprets accommodation, and sends signals via the Edinger-Westphal nucleus and the oculomotor nerve to the ciliary muscle, the medial rectus muscle and the sphincter pupillae muscle [20,21].…”

Oculomotor schwannoma causing a progressive complete third-nerve palsy

“…Of the cranial nerves, schwannomas arise in the vestibular nerve most commonly, followed by trigeminal, glossopharyngeal, vagal and facial nerves. Accessory, hypoglossal, oculomotor and abducens nerve schwannomas are rare 2 3. Schwannomas of the oculomotor nerve in particular are rarely isolated lesions; they are typically found alongside trigeminal nerve schwannomas as part of a hereditary tumour disease, such as neurofibromatosis type 2 2 3.…”