Wilbrand's knee: does it exist?

Nerve fibre organisation in the human optic nerve and chiasm: what do we really know?

A recent anatomical study of the human optic chiasm cast doubt on the widespread assumption that nerve fibres travelling in the human optic nerve and chiasm are arranged retinotopically. Accordingly, a scoping literature review was performed to determine what is known about the nerve fibre arrangement in these structures. Meta-analysis suggested that the average number of fibres in each optic nerve was 1.023 million with an inter-individual range of approximately 50% of the mean. Loss of nerve fibres with age (approximately 3,400 fibres/year) could not account for this variability. The review suggested that there might be a retinotopic arrangement of nerve fibres in the orbital portion of the optic nerve but that this arrangement is most likely to be lost posteriorly with a more random distribution of nerve fibres at the chiasm. Limited studies have looked at nerve fibre arrangement in the chiasm. In summary, the chiasm is more 'H-shaped' than 'X-shaped': nerve fibre crossings occur paracentrally with nerves in the centre of the chiasm travelling coronally and in parallel. There is interaction between crossed and uncrossed fibres which are widely distributed. The review supports the non-existence of Wilbrand's knee. Considerable further work is required to provide more precise anatomical information, but this review suggests that the assumed preservation of retinotopy in the human optic nerve and chiasm is probably not correct.

Endoscopic Endonasal Transsphenoidal Resection of Pituitary Adenomas in Patients Presenting With Monocular Blindness

BACKGROUND AND OBJECTIVES

Suprasellar tumors, particularly pituitary adenomas (PAs), commonly present with visual decline, and the endoscopic endonasal transsphenoidal approach (EETA) is the primary management for optic apparatus decompression. Patients presenting with complete preoperative monocular blindness comprise a high-risk subgroup, given concern for complete blindness. This retrospective cohort study evaluates outcomes after EETA for patients with PA presenting with monocular blindness.

METHODS

Retrospective analysis of all EETA cases at our institution from June 2012 to August 2023 was performed. Inclusion criteria included adults with confirmed PA and complete monocular blindness, defined as no light perception, and a relative afferent pupillary defect secondary to tumor mass effect.

RESULTS

Our cohort includes 15 patients (9 males, 6 females), comprising 2.4% of the overall PA cohort screened. The mean tumor diameter was 3.8 cm, with 6 being giant PAs (>4 cm). The mean duration of preoperative monocular blindness was 568 days. Additional symptoms included contralateral visual field defects (n = 11) and headaches (n = 10). Two patients presented with subacute PA apoplexy. Gross total resection was achieved in 46% of patients, reflecting tumor size and invasiveness. Postoperatively, 2 patients experienced improvement in their effectively blind eye and 2 had improved visual fields of the contralateral eye. Those with improvements were operated within 10 days of presentation, and no patients experienced worsened vision.

CONCLUSION

This is the first series of EETA outcomes in patients with higher-risk PA with monocular blindness on presentation. In these extensive lesions, vision remained stable for most without further decline and improvement from monocular blindness was observed in a small subset of patients with no light perception and relative afferent pupillary defect. Timing from vision loss to surgical intervention seemed to be associated with improvement. From a surgical perspective, caution is warranted to protect remaining vision and we conclude that EETA is safe in the management of these patients.

Wilbrand Knee Revisited

BACKGROUND

Over a century ago, German ophthalmologist Hermann Wilbrand reported inferonasal crossing fibers within the chiasm curve anteriorly into the contralateral optic nerve. This anatomic bend, "Wilbrand knee," is classically cited as the explanation for the "junctional scotoma," a contralateral superotemporal visual field defect associated with lesions affecting the optic nerve at its junction with the chiasm. More recent reports have called into question the existence of Wilbrand knee or suggested that it may simply be an artifact.

METHODS

Four human optic chiasms (obtained from cadaver donors with no reported premortem visual pathology) and 2 monkey chiasms were fixed and thin sectioned (40 µm), then examined using anisotropic scattering imaging, a novel technique that takes advantage of the fact that light reflects off well-defined linear structures (i.e., axonal tracts) in a predictable manner based on their orientation. Using this technique, tissue structures oriented in different directions can be distinguished at high resolution without the need for tissue staining.

RESULTS

In all 4 human optic chiasms, thin fiber tracts consistent with, but less prominent than, those Wilbrand had described were observed. No such tracts were found in the monkey chiasms.

CONCLUSIONS

Wilbrand knee exists in humans but is modest in its anterior projection. Wilbrand knee does not seem to be present in monkeys, however, which may explain conflicting reports in the literature regarding its existence.

Metastatic paraganglioma presenting as ajunctional scotoma

PURPOSE

To report a unique case of metastatic paraganglioma presenting as a junctional scotoma.

OBSERVATIONS

A 38-year-old Caucasian man with a history of abdominal paraganglioma presented with minimally blurred vision 20/25 visual acuity in the left eye. The patient was found to have a junctional scotoma upon visual field testing. Cranial MRI revealed a large peri-clival mass compressing the pre-chiasmal optic nerves and other loci of metastatic disease. Intracranial masses, including metastases, can present with a relatively intact central acuity and nonspecific visual symptoms.

CONCLUSIONS AND IMPORTANCE

To the best of our knowledge, this is the first report of metastatic paraganglioma causing a junctional scotoma. In cases with junctional scotoma, careful neuro-ophthalmic assessment and imaging are of paramount importance, even in patients with excellent visual acuity.

Cranio-Orbital Approach for Single-Stage En Bloc Resection of Optic Nerve Glioma: Technical Note

BACKGROUND AND IMPORTANCE

There is no consensus on the optimal surgical approach for managing optic nerve gliomas. For solely intraorbital tumors, a single-stage lateral orbitotomy approach for resection may be performed, but when the nerve within the optic canal is affected, two-stage cranial and orbital approaches are often used. The authors describe their technique to safely achieve aggressive nerve resection to minimize the probability of recurrence that might affect the optic tracts, optic chiasm, and contralateral optic nerve.

CLINICAL PRESENTATION

A 28-yr-old woman presented with painless progressive vision loss, resulting in blindness. The second of 2 transorbital biopsies was diagnostic and consistent with low-grade glioma. The lesion continued to grow on serial imaging. The patient was offered a globe-sparing operative approach, with aggressive resection of the lesion to minimize the probability of tumor recurrence, which could possibly affect vision in her contralateral eye. The patient did well postoperatively, with clean tumor margins on pathological analysis and no evidence of residual on imaging. On postoperative examination, she had a mild ptosis, which was nearly resolved at her 6-wk outpatient follow-up.

CONCLUSION

This aggressive single-stage en bloc resection of an optic nerve glioma can achieve excellent tumor margins and preservation of extraocular muscle function.

[Chiasmatic syndrome]

The optic chiasm is an essential anatomical structure in neuro-ophthalmology. The systematization of the visual pathways results from the arrangement of the retinal ganglion cell fibers. It explains the signs of chiasmal syndrome. A good knowledge of the anatomy permits to correlate visual field defects with imaging results. It is now possible to map the organization of the ganglion cell fibers within the chiasm. Their hemidecussation allows for stereoscopic vision in humans. The causes of chiasmal syndrome are multiple, but tumors and compressive causes predominate. The proximity of the pituitary region to the chiasm accounts for the frequency of chiasmal syndrome, which involves ophthalmologists not only through dysfunction of the visual pathway, which may be the presenting sign, but also through possible complications throughout the course of the disease. This review aims to synthesize the embryology, anatomy and principles of work-up for chiasmal syndrome as well as its many possible causes.

Junctional scotoma. A case report

The case concerns a 55 year-old female patient with progressive visual decrease in her right eye that showed a junctional scotoma in the visual field study. A magnetic resonance scan was performed, which showed a right middle cerebral artery aneurysm with ipsolateral chiasmatic involvement.

Utility of optical coherence tomography in the evaluation of sellar and parasellar mass lesions

PURPOSE OF REVIEW

Anterior visual pathway compression is a common feature of sellar region masses. We review the visual pathway neuroanatomy pertaining to sellar and parasellar lesions and describe recent advances in optical coherence tomography (OCT) imaging that have provided a novel quantitative perspective in the evaluation and management of such patients.

RECENT FINDINGS

Ultrastructural measurements of optic nerve integrity using OCT, namely peripapillary retinal nerve fiber layer (pRNFL) and the ganglion cell and inner plexiform layer (GCIPL) thicknesses, have been shown to correlate with visual acuity and visual field deficits on perimetry in patients with compressive sellar region masses. In some cases, OCT can visualize early signs of anterior visual pathway involvement in the absence of clinically evident visual field loss or optic disc pallor. OCT is particularly useful when assessing patients who demonstrate less reliable visual field testing. Furthermore, there is growing awareness that pRNFL and GCIPL thinning preoperatively correlate with worse visual recovery following chiasmal decompression, highlighting the prognostic utility of OCT in this patient population.

SUMMARY

OCT provides a complimentary, yet critical, role in quantitatively assessing ultrastructural retinal injury in patients with sellar and parasellar lesions compressing the anterior visual pathway and should be incorporated into routine evaluation.

The visual pathway--functional anatomy and pathology

Visual failure of any kind is a common clinical presentation and indication for neuroimaging. Monocular deficits should concentrate the search to the anterior (prechiasmatic) visual pathway. Bitemporal hemianopia suggests a chiasmatic cause, whereas retrochiasmatic lesions characteristically cause homonymous hemianopic defects. Quadrantanopias usually arise from lesions in the optic radiations. Disorders of visual perception can be broadly divided into "where" and "what" problems caused by lesions in the parietal and temporal lobes, respectively, and their associated white matter tracts. Visualization of the retrochiasmatic visual and visual association pathways is aided by diffusion tensor imaging.

Hemangioblastoma of the optic nerve producing bilateral optic tract edema in a patient with von Hippel-Lindau disease

BACKGROUND

The authors present a novel case of a hemangioblastoma of the optic nerve producing bilateral optic tract edema in a patient with von Hippel-Lindau disease (VHL). This is the only case in the literature documenting optic tract edema secondary to a hemangioblastoma of the optic nerve.

CASE DESCRIPTION

The patient was a 34-year-old female in whom this lesion was causing retro-orbital pain and proptosis. She had previously lost vision in the symptomatic eye secondary to a retinal hemangioblastoma. The optic nerve lesion was excised by sectioning the optic nerve both proximally and distally to the lesion. There were no complications and patient's symptoms resolved postoperatively. A follow-up magnetic resonance imaging (MRI) scan revealed complete excision of the mass and resolution of the optic tract edema.

CONCLUSION

Optic nerve hemangioblastomas in patients with VHL are rare, but are manageable with meticulous microneurosurgery and with appropriate patient expectations. This is the first known case of an optic nerve hemangioblastoma producing bilateral optic tract edema, which resolved after resection of the prechiasmal tumor. Hemangioblastoma should remain in the differential diagnosis of optic nerve tumors, especially in the setting of VHL.

Pre-chiasmatic transection of the optic nerve can save contralateral vision in patients with optic nerve sheath meningioms

OBJECTIVES

With respect to its characteristic pattern of growth from the orbit into the intracranial space toward the chiasm, patients with optic nerve sheath meningiomas (ONSM) are threatened to loose function of both optic nerves. Fortunately, in less than 5% both optic nerves are involved initially. Hence, prevention of vision of the contralateral eye is the foremost aim of any therapy. Performing pre-chiasmatic transection might offer a further treatment option to avoid further tumor growth toward the chiasm.

PATIENTS AND METHODS

In this retrospective study 12 patients with ONSM and blindness of the affected eye were included. The surgical approach was performed either from pterional intradural or as a combined approach from pterional extra- and intradural.

RESULTS

Without any exceptions, vision of the contralateral eye could be preserved and did not show any deterioration after surgery or during the follow-up time of 50.6 months. Furthermore in 58.3% of patients gross total tumor resection could be achieved. During follow up observation in 67% of patients no further tumor progress or recurrences could be observed. 4 patients, however, showed delayed tumor progress or recurrences that were treated by radiotherapy.

CONCLUSION

Pre-chiasmatic transection of the optic nerve might offer a surgical treatment option to control tumor growth and to preserve vision of the contralateral eye.

The chiasmal spur

A 51-year-old woman underwent craniotomy for removal of a pituitary tumor. At surgery, anomalous tissue was found projecting forward from the anterior angle of the optic chiasm. Termed "the chiasmal spur," this anomaly has been described previously in 5 patients, all as an incidental finding at autopsy. Our case is the first instance of the chiasmal spur being discovered and photographed intraoperatively.

Morphologie des Chiasma opticum bei Albinismus

Albinism is associated with a misrouting of fibers at the optic chiasm where the majority of fibers cross to the contralateral side. The cause of this abnormal decussation pattern reflects a disturbance of cell cycle regulation in the development of the retina which is in part controlled by melanin. Growing axons from retinal ganglion cells therefore arrive later than usual at the optic chiasm and are misrouted contralaterally. This atypical decussation leads to morphological changes of the optic chiasm including a reduced chiasm width with larger angles between optic nerves and tracts which can be shown by magnetic resonance imaging.