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Clinical case: Optic neuropathy due to optic nerve compression: want to learn more about it?

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Clinical case: Optic neuropathy due to optic nerve compression

In this article, we describe a case of a woman who presented with progressive deterioration of visual function in her left eye. Her diagnosis was left optic neuropathy, but what was the cause of her pathology? Stick around to find out the answer, and more details about her examinations, investigations, as well as the management strategy, and evolution. You will also learn about the anatomical knowledge pertinent to this clinical case.

After reviewing this case you should be able to describe the following:

  • The functional anatomy and pathway of the optic nerve.
  • The clinical relationship between tumors of the sella turcica and the optic nerve.
  • What is meant by a pterional craniotomy; the clinical importance of the pterion.
Key facts
Optic nerve pathway Ganglion cells of retina (optic head) -> orbital part -> optic canal -> middle cranial fossa (cranial part) -> optic chiasm -> optic tract -> lateral geniculate body of thalamus -> optic radiation -> visual cortex
Vision dysfunctions

Impingement distal to the optic chiasm -> vision defects only in ipsilateral eye

Pressure on the optic chiasm -> bitemporal defects

Impingement proximal to the optic chiasm -> vision defects in both eyes

Pterional craniotomy Neurosurgical approach to the middle cranial fossa, anterior cranial fossa, suprasellar and parasellar structures, and the Circle of Willis via the pterion.

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

Case description

History and examination

Figure 1. Results of left visual field examination showing visual perception only in superonasal quadrant. 

The patient was a 50-year-old woman with no pertinent prior disease; she was referred to the Neurosurgery Department for progressive deterioration of visual function in her left eye of 3-4 months duration. Serial visual field examination of the left eye showed a loss of three visual quadrants, with only the superonasal quadrant showing significant remaining visual function (Figure 1). The right visual field was normal, suggesting the patient had a left optic neuropathy.

Imaging

T1 contrast MRI revealed a sella turcica meningioma (tumor arising from the dura overlying sella turcica) measuring approximately 1.7 cm × 1.9 cm × 1.3 cm that was presumably compressing the left optic nerve (Figure 2).

Figure 2. Coronal T1 MRI depicting tumor and surrounding structures.

Management and surgery

The patient underwent a left pterional craniotomy (Figure 3). The dura was opened and the Sylvian fissure was expanded. Upon elevating the left frontal lobe, the tumor became visible. Further examination showed that the tumor was compressing the nerve on its medial side whereas the initial part of the A1 segment of the anterior cerebral artery (ACA) was compressing it on its lateral side (Figure 4).

Figure 3. A. Lateral view of the skull with the individual skull bones in different colors. The approximate incision line for a pterional craniotomy is shown as is the skull region known as pterion. B. View of interior skull base showing the lesser wing of sphenoid and the superior orbital fissure, both of which are critical landmarks in the pterional craniotomy (see text).

The tumor was then internally decompressed, and the ACA separated from the nerve. Once the tumor was extirpated, the nerve became freely movable. The patient recovered well from the procedure well and was discharged one week postoperative.

Evolution

A complete neuro-ophthalmologic evaluation performed seven days after surgery revealed best-corrected visual acuity of 0.8 (mild visual loss) in both eyes with no relative afferent pupillary defect (no difference in the response of the eyes to bright light). Examination of the right eye showed a normal pink disc, whereas in the left fundus there was pallor (paleness) of the temporal part of the optic disc (indicating some remaining damage to the left optic nerve, which is consistent with the mild loss). The right visual field was normal, whereas in the left visual field there was still central scotoma (dark spot) and some temporal field depression.

Follow-up visual field examination performed ten months after surgery showed again a normal right visual field but a solitary paracentral scotoma in the left visual field, indicating that the left optic nerve had sustained some permanent damage. There was, however, no evidence of residual tumor on MRI performed six months after surgery.

Figure 4. A. High magnification photograph of the left orbit and sella turcica region in a cadaver; this view is similar to that would be available to the surgeons, albeit without the removal of the orbital roof. In A the tumor (white dashed circle) is drawn in and reduced in size so that the surrounding anatomy can be seen. The anterior cerebral artery (ACA), which has also been drawn in, is shown originating from the internal carotid artery (ICA) and crossing over optic nerve (lateral to medial) and as it does so, acting as a boundary to the nerve, preventing the nerve from moving in response to the tumor. The tumor is shown compressing the nerve on its medial side so that the nerve is thus being strangulated from both sides. In the surgical procedure described in this report, the tumor was removed and nerve freed from the artery. C is a cadaver dissection of the entire extent of the left optic nerve from the eyeball to the optic chiasm. The bony walls of the optic canal have been removed. C is courtesy of Dr. John Selhorst. TS, sella turcica. MC, middle cerebral artery.

Surgical and anatomical considerations

This case describes a patient with optic nerve strangulation by the A1 segment of the ACA in a patient because of the presence of a sella turcica tumor. Once the tumor was debulked, the optic nerve was seen to have been compressed between the tumor and the artery. The preoperative neuro-ophthalmic examination had shown a significant deficit in the left visual function, which dramatically improved immediately after surgery (but which still remained less than normal). Visual loss resulting from mechanical compression of the optic nerve by tumors, particularly by sella turcica meningiomas is well established, and vascular elements (e.g. ACA as in this case) may play a significant role in the mechanism of this compression.

The left ACA is one of a pair of arteries that supplies most midline portions of the frontal lobes of the brain and superior medial parietal lobes. Both of the anterior cerebral arteries arise from the respective internal carotid arteries and are part of the circle of Willis (Figure 5).

Figure 5. The large image shows a magnified cadaver photograph of the Circle of Willis. The smaller image shows where the Circle is located at the base of the brain.

The A1 segment of the ACA, which is the segment of interest for this case, originates from the internal carotid artery and extends to the anterior communicating artery, which connects the left and right arteries. The circle of Willis (circulus arteriosus cerebri) is a collection of arteries that are located at the base of the brain. The “circle” was named after Thomas Willis by his student, Richard Lower. Willis authored, Cerebri Anatome, which described and depicted this vascular ring of arteries. The circle of Willis encircles the stalk of the pituitary gland and provides a connection between the internal carotid and vertebrobasilar arterial brain supply systems. The circle of Willis is formed when each of the internal carotid arteries divides into the anterior cerebral artery and the middle cerebral artery. The anterior cerebral arteries are then united by an anterior communicating artery. Posteriorly, the basilar artery branches into a left and right posterior cerebral artery, forming the posterior circulation. The circle of Willis is completed by the posterior communicating arteries, which join the posterior and internal carotid arteries.

Figure 6. Arteries of the brain (inferior view)

Clinical case: Optic neuropathy due to optic nerve compression: want to learn more about it?

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“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

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