Binasal hemianopia caused by pneumosinus dilatans of the sphenoid sinuses.

Bitemporal hemianopia is a significant pathological hallmark of a pituitary lesion; however, binasal hemianopia is rarely reported, except for its known association with other ocular diseases rather than with brain lesions. We report a 24-year-old male with binasal hemianopia caused by pneumosinus dilatans of the sphenoid sinuses.

Binasal hemianopia is uncommon, and is associated with other ocular diseases rather than with brain lesions.[123] Pneumosinus dilatans (PSD) is a rare condition in which dilated paranasal sinuses lined by normal mucosa are filled with air.[4] The possibility of PSD of the sphenoid sinus is important to consider visual problems because of its close proximity to the optic nerve in the optic canal.[5] We present the case of a 24-year-old male with binasal hemianopia caused by PSD of the sphenoid sinuses.

Case Report

A 24-year-old male presented to our clinic with a bilateral visual disturbance that had been gradually worsening for several months. There was no previous history of systemic diseases, ocular trauma, amblyopia, or regularly taking medication. He did not have any family history of visual problems. He had previously experienced intermittent mild headaches in the frontal area. The best-corrected visual acuity was 20/100 in both eyes, and the refractive error was − 600 + 2.50 diopters (D) × 90 in the right eye and − 6.00 + 2.00 D × 90 in the left eye. The pupil showed a normal response to light and near stimulation in both eyes. The color vision test using the Ishihara plate showed normal results. There was no ocular motility deficit. The intraocular pressures were 20 mmHg in the right eye and 19 mmHg in the left eye. A fundoscopic examination showed a normal finding of optic discs in both eyes [Fig. 1a and b]. The automated perimetry (Humphrey field analyzer, Carl Zeiss Meditec, Dublin, CA, USA) demonstrated binasal hemianopia [Fig. 2a and b]. The repeated visual field test performed 2 weeks later showed the same results. The multifocal electroretinography performed at another clinic showed normal results. Magnetic resonance imaging of the brain revealed extensively pneumatized and enlarged ethmoid and sphenoid sinuses. The intracanalicular portion of the optic nerve was compressed in the temporal region by the enlarged sphenoid sinuses in each eye [Fig. 3a-d]. The patient was referred to the otorhinolaryngology department for surgical decompression; however, he refused the surgical procedure and did not return for follow-up visits.

Figure 1

Fundus photograph taken at the initial visit. (a) Right eye. (b) Left eye

Figure 2

An automated visual field test (Humphrey field analyzer, Carl Zeiss Meditec, Dublin, CA, USA) showed binasal hemianopia. (a) Visual field of the left eye. (b) Visual field of the right eye

Figure 3

(a) Coronal view of the magnetic resonance imaging (MRI) results of the brain revealed extensively pneumatized and enlarged ethmoid and sphenoid sinuses (arrow). (b and c) Axial view of the brain MRI results revealed that the intracanalicular portion of the optic nerve was compressed in the temporal region by the enlarged sphenoid sinuses in each eye (arrow). (d) Axial view of the brain MRI results shows normal optic chiasm (arrow)

Discussion

This is the first report of binasal hemianopia caused by PSD of the sphenoid sinus. When considering the visual pathway from the retina to the occipital lobe, binasal hemianopia can result from damage to the temporal aspects of both optic nerves.[6] Hamann et al. reported binasal hemianopia extending across the vertical midline due to bilateral internal carotid artery atherosclerosis.[7]

In the present case, the temporal aspect of the intracanalicular segment of the optic nerve, containing the fibers from the nasal visual field, was compressed by the enlarged sphenoid sinuses in each eye. Macular sparing of the visual field was indicated because fibers from the papillomacular bundle gradually move centrally in the more posterior portions of the optic nerve.[6] Therefore, these fibers may be less vulnerable to the temporal aspect of pneumatic compression. PSD is a rare condition in which dilated paranasal sinuses lined by normal mucosa are filled with air.[45] The exact mechanism underlying the origin of PSD is unknown, but a ball-valve theory suggesting that PSD is caused by an inflammatory process within the sinus or another source of pressure has been proposed.[5] The frontal sinus is the most commonly affected sinus, but the sphenoid sinus is the most important because of its close proximity to the optic nerve in the optic canal.[5] Various visual symptoms can be caused by PSD of sphenoid sinus.[458] These symptoms include gradual painless visual loss, recurrent transient visual loss, and even sudden visual loss.[4578] Approximately 1 mm of the optic canal wall separates the optic nerve from the sinus cavity. Excessive pneumatization can lead to thinning and gross dehiscence of the canal wall and result in compression of the optic nerve.[6] In about 4% of patients, the optic nerves have areas covered only by the nerve sheaths and sinus mucosa, but without any bony wall separating the intracanalicular portion of the optic nerve from the adjacent paranasal sinus.[6] In this case, the optic nerve may have been more susceptible to the local force caused by PSD. In patients with PSD of the sphenoid sinus, the most common symptom is a visual disturbance, but not nasal symptoms such as nasal obstruction, nasal discharge, or sinusitis.[4] The sphenoid sinus, when involved, has not only the highest rate of associated conditions among all sinuses, but also has the most severely associated conditions.[8] The conditions most commonly associated with PSD of the sphenoid sinus are meningioma, arachnoid cyst, and hydrocephalus.[48] Fortunately, these associated medical conditions were ruled out in our case by neuroimaging. It will be necessary to consider the possibility of concomitant conditions in the evaluation of patients with PSD of the sphenoid sinus.

The repeated visual field test should be performed in patients with unusual visual field defects, because the visual field test can be affected by various factors such as the eyelid, refractive correction, and the patient's cooperation.[6] With our case, we also performed repeated visual field tests to confirm the results.

A patient with compressive optic neuropathy usually shows decreased color vision.[69] However, our case had no abnormal findings using the color vision test. It is possible that a color vision defect was not detectable, because the Ishihara test screens only for red and green color deficiency, is not effective in grading the severity of the color defect, and has limitations in determining the extent and type of deficiency.[10] There are many patients with profound optic nerve dysfunctions that may perform relatively well in color plate testing.[9]

The optic discs of patients with compressive optic neuropathy may appear normal or show variable degrees of pallor.[69] We postulated that in this case, pallor of the disc was not yet evident because of the early stage of the condition.

In conclusion, binasal hemianopia can be caused by PSD of the sphenoid sinus. Although symptomatic patients with PSD of the sphenoid sinus are uncommon, the most common symptom of PSD is visual loss. PSD of the sphenoid sinus should be considered in the diagnosis of patients with atypical visual disturbances.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.