Non-Invasive Detection of Recurrent Intracranial Pressure via Optical Coherence Tomography: A Case Report

Introduction

Papilledema is a common sign of high intracranial pressure (ICP). It results from axoplasmic flow stasis at the optic nerve head, leading to nerve edema from pressure on the nerve behind the eye. Continued high pressure can result in abnormalities of axonal transport, causing loss of axons and eventual optic atrophy secondary to intraneuronal ischemia [1,2]. Detecting relapse of high ICP is difficult because once optic nerve atrophy is present, re-swelling of the optic nerve head is not expected to be visible on fundoscopy as a result of axoplasm loss and axonal death (“dead fibers don’t swell”) [1,2]. Moreover, the symptoms of headache and visual disturbances are non-specific and can be chronic after an episode of high ICP. The consensus guidelines state that optic nerve examination is essential for intracranial hypertension diagnosis in patients with acute exacerbation of headache, and in those found not to have papilledema further invasive investigation with lumbar puncture or brain imaging is not required unless other secondary causes are suspected [3]. Undetected intracranial hypertension can lead to visual loss, increased irritabilities, learning difficulties, or even mental retardation, and seriously affect the quality of life due to headache [4,5]. In children, the most common cause is venous hypertension manifesting as communicating hydrocephalus [6]. Ventriculoperitoneal shunts are used to treat intracranial hypertension by removing excess cerebrospinal fluid from the peritoneal cavity, the atrium, or the pleura [4]. The long-term complication of the shunt might be its malfunction [4,7,8] which is a relatively common problem (the failure rate is above 30%) [9]. Therefore, it is important find a fast and safe examination that can help distinguish patients requiring immediate help from those who can receive only observation. Optical coherence tomography (OCT) is a widely used non-invasive imaging technique for diagnosing and monitoring many ophthalmic diseases [10]. It provides real-time cross-sectional images of the optic nerve head [10]. Many studies have shown that measurement of the peripapillary retinal nerve fiber layer (pRNFL) in OCT is valuable for assessing papilledema, as it is strongly correlated with fundoscopy and Frisen grading [11,12]. High ICP relapsing without visible papilledema and the role of OCT in diagnosis have been described in the literature [12–15]. This report describes the case of a 23-year-old woman with a ventriculoperitoneal shunt implanted at the age of 11 years due to idiopathic hydrocephalus presenting swelling of pRNFL on OCT without visible papilledema.

Case Report

A 23-year-old woman with a ventriculoperitoneal shunt implanted at the age of 11 due to idiopathic hydrocephalus, drug-resistant epilepsy, and juvenile idiopathic arthritis reported to our ophthalmology outpatient clinic due to headaches, nausea, and visual disturbances consisting of deterioration of the distance best corrected visual acuity (BCVA) and “blue dots” seen after exercising. She had already had a neurological examination, both eyes’ fundus evaluation that revealed optic nerve pallor without clinically visible disc edema, and magnetic resonance imaging (MRI) of the head (patient’s documentation). Neurologists did not treat her because results did not reveal any signs of increased intracranial pressure. We decided to repeat and extend the ophthalmological examination, which confirmed partial atrophy of the optic nerves (more prominent in the left eye). In addition, there were hard exudates arranged radially around the nasal part of the fovea in the right eye (Figure 1, white arrow), which could indicate blood-retinal barrier disruption due to papilledema. The distance best corrected visual acuity was 0.6 according to Snellen in the right eye and counting fingers/hand motion in the left eye. An optical coherence tomography examination revealed swelling of pRNFL in the right eye and a lower borderline result for the left eye (Figure 2). However, the patient showed us the written result of the ophthalmological examination from 6 months prior, showing the distance BCVA of the right eye was significantly better (1.0) and there was no pRNFL elevation on OCT (patient’s documentation). Due to a recent neurological examination and MRI imagining of the head that excluded the recurrence of intracranial hypertension or other emergency situations, the patient remained under ophthalmological observation waiting for an appointment date in the neurological outpatient clinic. However, when bilateral abducens nerve palsy occurred days later (Figure 3), she was referred again to the neurological emergency ward, receiving a preliminary diagnosis of severe high ICP due to shunt malfunction as the most probable cause of her reported signs and symptoms. At the neurological emergency ward, a lumbar puncture was performed, and elevated opening intracranial pressure was revealed (there was no information on ICP value in the patient’s documentation from the neurological ward). Some cerebrospinal fluid was removed to temporarily reduce the intracranial pressure before subsequent shut revision. After the procedure, all her symptoms were resolved. Ophthalmological examination showed a gradual improvement of distance BCVA to 1.0 according to Snellen in the right eye, regression of retinal exudates (Figure 4), pRNFL swelling (Figure 5), and paralysis of the abducens nerves.

Discussion

Our case report shows that swelling of pRNFL in OCT can be detected in patients with the recurrence of high ICP despite optic disc atrophy shown by the fundus examination. This information is valuable because detecting relapses is difficult since there is no objective way of monitoring it other than invasive intracranial monitoring [12]. The reported patient concerns and symptoms are usually non-specific. The guidelines recommend that patients with exacerbation of headaches should have an ocular examination to determine the presence of papilledema before performing any invasive tests [3]. The literature shows that papilledema can be clinically undetectable on fundoscopy in the presence of optic nerve atrophy [1,2]. In these cases, diagnosis of recurrent intracranial hypertension is difficult. Therefore, there is an urgent need for quick, accessible, and preferably non-invasive examinations that distinguish urgent patients from those who can be left for observation. Optical coherence tomography seems to meet these criteria. In our case, OCT revealed a visible pRNFL thickness rise above normal values in the right eye and a slight elevation compared to the baseline in the left eye, despite a lack of papilledema on fundoscopy. These results, together with the patient’s symptoms and bilateral paralysis of the abducens, led us to the diagnosis of a shunt malfunction. Quick implementation of invasive treatment and ICP reduction to the normal value protected the patient from further vision loss, which had already irreversibly deteriorated after the first episode of intracranial hypertension in childhood. The occurrence of intracranial hypertension relapsing without visible papilledema and the role of OCT in detecting a shunt malfunction have been described in previous case reports. Qureshi et al [13] presented a case series of 3 patients who had shunt surgery for idiopathic intracranial hypertension and optic atrophy before the recurrence of increased ICP due to shunt malfunction. In 1 of the 3 patients, the papilledema was clinically undetectable on dilated slit lamp examination. However, there was still an appreciable rise in the pRNFL thickness on OCT. Yamanuha et al [14] described a case of a 34-year-old woman with a history of optic atrophy secondary to intracranial hypertension after an episode of meningitis. At the recurrence of intracranial hypertension, there were diffuse optic nerve pallor with mild blurring of the disc margins bilaterally on fundus examination and diffuse pRNFL thickening with nasal retinal edema and subretinal fluid in both eyes on OCT. After implantation of a lumboperitoneal shunt, the optic disc and macular edema quickly resolved. Huang-Link et al [12] investigated the role of OCT in the monitoring idiopathic intracranial hypertension with and without papilledema, and concluded that OCT is sensitive and reliable for diagnosing even slightly increased ICP. Although no significant difference was seen in pRNFL thickness compared to results obtained from 9 patients with remitting idiopathic intracranial hypertension without papilledema and 19 controls (patients with other neurological diseases), rim area and rim thickness were significantly increased, while cup-to-disc volume was decreased in the former. Increased pRNFL thickness was observed only in patients with papilledema, and only this parameter changed after therapeutic cerebrospinal fluid removal. The reason why our patient showed increased pRNFL thickness during the episode of raised ICT might be the fact that, although we did not know the specific number of the opening pressure, she probably had severely elevated ICP as there was bilateral abducens nerve palsy present. The mean ICP in the study by Huang-Link et al was 31±5 cmH2O (range 25–38, normal value < 25 cmH2O) without neurological deficit, which could classify their intracranial hypertension as mild or moderate. Moreover, the present case report suggests the degree of optic nerve atrophy before the recurrence of raised ICP can influence further pRNFL elevation. In our patient’s right eye, where there was less atrophy, there was a visible pRNFL elevation during the episode of increased ICP, while in the left eye, where atrophy was profound initially, the change in pRNFL thickness was less marked. In a recent study, Xie et al [15] performed a retrospective chart review to evaluate whether papilledema recurrence can be detected in a population of patients with idiopathic intracranial hypertension and optic atrophy using OCT. Atrophy was classified as moderate if the average pRNFL thickness was ≤80 μm and as severe if it was ≤60 μm on at least 2 consecutive OCT scans. Among 36 episodes of intracranial hypertension recurrence, 17 (47.3%) occurred in patients with both clinical and OCT evidence supporting relapse; 12 (33.3%) occurred in patients with OCT changes but no clinical signs and symptoms, and 7 (19.4%) occurred in patients with clinical signs but no OCT changes. The rate, magnitude, and concordance of pRNFL swelling were similar between moderately versus severely atrophic eyes. Our patient had a visible difference between the magnitude of pRNFL thickness increase between the right and left eyes. The reason for this observation is probably the fact that our patient’s right optic nerve was not atrophic according to pRNFL (average 90 μm), while the left was moderate atrophic (average 68 μm), although both optic discs had pallor on fundoscopy. Xie et al [15] found that if there is a sufficient volume of viable axons, optic disc edema may be visible on ophthalmoscopy even in atrophic nerves. However, higher ICP is required to cause detectable effects. That is why OCT is especially helpful in patients who do not have clinical symptoms or signs of relapse, because pRNFL thickening may be the first or only indication of recurrently increased ICP. However, relapse of intracranial hypertension can also occur without OCT changes, which makes this examination important, but only when used for diagnosis in combination with other methods.

Conclusions

Optical coherence tomography is a quick, non-invasive, sensitive, and objective in vivo method for monitoring the recurrence of increased ICP and treatment response. The measurements are easy to perform, the technique can be learned quickly, and the repeatability of scans is high. Despite the relatively high cost of the equipment, OCT is available in most ophthalmological outpatient clinics. Optical coherence tomography imaging should be performed in all cases suspected of intracranial hypertension when an ophthalmological examination does not reveal papilledema, especially in all cases with optic atrophy. It is also a valuable tool for monitoring the effectiveness of treatment.