Papilledema is swelling of the optic nerve head (optic disc), secondary to elevated intracranial pressure (ICP) . It is usually bilateral. Optic disc edema in the absence of elevated ICP is commonly referred to as “disc swelling”, which is usually associated with ocular diseases like optic neuritis and ischemic optic neuropathy. However, patients with bilateral optic disc swelling should be suspected of having an elevated ICP, whether or not they have neurological manifestations. Causes of elevated ICP include obstruction of the ventricular system by congenital or acquired lesions, space-occupying intracranial lesions, subarachnoid hemorrhage, cerebral trauma, cerebral venous sinus thrombosis/stenosis, and idiopathic intracranial hypertension.
Elevated ICP usually causes dramatic neurological symptoms, including headaches, nausea, vomiting and deterioration of consciousness, as well as visual impairment. Such patients are most commonly diagnosed in the neurology department. However, chronic cerebral venous sinus occlusion (CVSO), either complete or partial, can cause chronically elevated ICP, and can produce visual impairment as the only clinical symptom. Thus such patients often present to the optometrist or ophthalmologist. As well as producing decreased visual acuity, chronic papilledema induced by elevated ICP can produce visual field defects if the optic disc edema persists. However, unlike primary optic nerve diseases like optic neuritis, the flash VEP in patients with papilledema secondary to elevated ICP is often normal or only mildly affected [5, 6].
In case 1, the symptoms, other than blurred vison, were relatively occult. Although the bilateral optic disc swelling strongly indicated elevated ICP, there were no positive findings on CT or MRI. However, vision was not improved following treatment with systemic steroids. Therefore, further investigation was performed, which demonstrated elevated ICP secondary to right sigmoid sinus thrombosis. In retrospect, the patient’s history of mastoiditis and surgery eight years prior was highly significant. Mastoiditis is an important cause of sigmoid sinus thrombosis, especially in younger patients.
In case 2, the patient was a septuagenarian male with a long history of impaired vision, but no neurological symptoms. Due to the likely chronicity of the elevated ICP at presentation, the optic disc swelling in the right eye was not prominent, and the optic nerve in the left eye was already slightly atrophied, and the eye was blind. Prior to ophthalmology consultation, his visual impairment may be partially attributed to his multiple lacunar cerebral infarctions. But this multiple lacunar cerebral infarction as Fig. 3 showed can’t explain the severity of his visual impairment of both eyes, which indicated that the cerebral infarctions did not distinctly affect his visual pathway. Given his age, a diagnosis of non-arteritic anterior ischemic optic neuropathy was also made. However, the severity of visual impairment and lack of response to steroid therapy indicated the need for further investigation. Following MRV imaging, a diagnosis of superior sagittal sinus thrombosis was made. The patient’s visual impairment improved following endovascular stenting of the venous sinus.
Case 3 was that of a young adult female with blurred vision and bilateral papilledema, but no other neurological symptoms, and no history of systemic disease or infection. Her elevated ICP was confirmed by lumbar puncture, but unlike the other two cases, her radiological findings were less prominent. There were no definite signs of sinus thrombosis observed from the MRV, but a narrowed section was noted at the junction between the right transverse and sigmoid sinus. With no evidence of any intracranial mass, the patient was diagnosed with right transverse sinus stenosis. However, the etiology of this stenosis is currently still unknown, and the patient is under continued management by the neurosurgical team.
CVSO (partial or complete) affects the dural venous sinuses that drain blood from the brain, and is usually caused by either venous thrombosis or stenosis. Cerebral venous sinus thrombosis (CVST) most commonly affects the transverse sinus (86% of cases), followed by the superior sagittal sinus (62%), straight sinus (18%), then least commonly, the cortical veins (17%) . Risk factors for CVST include thrombophilia, chronic inflammatory diseases, use of hormonal contraception, infections such as meningitis, mastoiditis and sinusitis, and invasive procedures in the head and neck area [7, 8]. Symptoms of CVST include headache, visual impairment, symptoms of stroke (such as unilateral limb and facial weakness), and seizures. However, neurological symptoms are absent in a notable proportion of patients, and these patients may present later with impaired visual acuity due to chronic, advancing papilledema [9, 10].
Cerebral venous sinus stenosis (CVSS) is a rare intracranial abnormality. Stenosis may be caused by abnormal intrinsic dural sinus anatomy or by extrinsic compression; for example, due to an intracranial tumor or enlarged arachnoid granulation. In many cases the cause of stenosis is unknown. The stenosis is most often found at the junction of the transverse and sigmoid sinuses, and is typically diagnosed by venography [11, 12]. Regardless of the underlying cause, stenting has proved (in multiple retrospective, non-controlled studies) to be an effective method for improving the symptoms of elevated ICP and papilledema [13, 14].
Imaging of patients with CVSO, using unenhanced CT or MRI, may demonstrate gross abnormalities, such as cerebral edema, venous infarction and dilated ventricles. However in some cases, unenhanced imaging may be totally normal, especially in patients with a chronic disease course. Therefore, when elevated ICP is suspected, contrast-enhanced MR venography is required to image the cerebral veins for thrombus or stenosis, and lumbar puncture (LP) may be needed, to measure the opening pressure and test for constituent changes in the CSF.
In summary, CVST and CVSS (here collectively referred to as CVSO) are severe conditions which can cause elevated ICP, leading to visual impairment. A considerable amount of patients with CVSO have no apparent neurological symptoms other than visual loss. VEP could be normal or abnormal. When encountering patients with bilateral papilledema, especially those with normal unenhanced brain imaging, CVSO should always be considered. Further investigations such as LP, MRV or DSA are necessary to diagnose or rule-out CVST or CVSS.