Imaging of Cranial Nerves III, IV, VI in Congenital Cranial Dysinnervation Disorders

Abstract

Congenital cranial dysinnervation disorders are a group of diseases caused by abnormal development of cranial nerve nuclei or their axonal connections, resulting in aberrant innervation of the ocular and facial musculature. Its diagnosis could be facilitated by the development of high resolution thin-section magnetic resonance imaging. The purpose of this review is to describe the method to visualize cranial nerves III, IV, and VI and to present the imaging findings of congenital cranial dysinnervation disorders including congenital oculomotor nerve palsy, congenital trochlear nerve palsy, Duane retraction syndrome, Möbius syndrome, congenital fibrosis of the extraocular muscles, synergistic divergence, and synergistic convergence.

Keywords: Congenital fibrosis of the extraocular muscles; Congenital trochlear nerve palsy; Duane retraction syndrome; Möbius syndrome; Oculomotor nerve palsy.

Fig. 1. Normal cranial nerve (CN) III and VI. (A) Axial magnetic resonance image at the level of the lower midbrain shows the cisternal segments of CN III (arrows) as linear dark structures coursing in the anterolateral direction toward the cavernous sinus. (B) Axial magnetic resonance image at the pontomedullary junction shows the cisternal segments of CN VI (black arrows) coursing in the anterosuperior direction toward Dorello's canal. CN VII (double arrow) and CN VIII (white arrows) are also well identified.

Fig. 2. Normal cranial nerve IV. Axial magnetic resonance image at the level of the inferior colliculus shows the cisternal segments of cranial nerve IV (thin arrows) exiting from the posterior aspect of the brainstem and coursing in the anterolateral direction toward the tentorium (thick arrows).

Fig. 3. Congenital cranial nerve (CN) III agenesis. (A) Ocular versions show limited elevation, adduction, and depression of the right eye. (B) Axial magnetic resonance image shows normal left CN III (arrow). Right CN III is not observed. (C) Orbital coronal magnetic resonance image shows atrophy of the right medial rectus and right inferior rectus (arrows).

Fig. 4. Congenital cranial nerve (CN) IV agenesis. (A) Ocular versions show right hypertropia and limited depression both in downgaze and adduction in the right eye. (B) Axial magnetic resonance image shows normal left CN IV (arrows). Right CN IV is not identified. (C) Orbital coronal magnetic resonance image shows atrophy of the right superior oblique muscle (arrow). Compare with the left superior oblique (double arrow).

Fig. 5. Duane's retraction syndrome type 1. (A) Ocular versions show limitations of adduction and abduction and fissure narrowing on adduction in the left eye. (B) Axial magnetic resonance image at the pontomedullary junction shows normal right cranial nerve VI (arrow). Left cranial nerve VI is not identified.

Fig. 6. Bilateral Möbius syndrome. (A) Ocular versions show limitation on abduction in both eyes. (B) Axial magnetic resonance image at the lower pons shows normal cranial nerve VIII bilaterally (white and black arrows). Cranial nerve VI and VII are not observed bilaterally. Refer to normal VI and VII in Fig. 1B.

Fig. 7. Congenital fibrosis of the extraocular muscles in both eyes. (A) Ocular versions show limited ductions of both eyes. (B) Axial magnetic resonance image shows bilateral small-sized cranial nerve III (arrows), suggesting hypoplasia. (C) Orbital coronal magnetic resonance image shows mild atrophy of the right superior rectus and right medial rectus and severe atrophy of the left superior rectus and left medial rectus (arrows).