Keywords
intracranial hypertension - ultrasonography - optic nerve sheath
Palavras-chave
hipertensão intracraniana - ultrassonografia - bainha do nervo óptico
Introduction
Intracranial hypertension (ICH) is a frequent complication in patients with neurological
disorders, and it is associated with high morbidity and mortality. As such, its early
diagnosis and the institution of adequate therapeutic measures are fundamental for
a good prognosis.[1] These patients often require multimodal monitoring of the intracranial pressure
(ICP), of the cerebral perfusion pressure (CPP), of the metabolism and tissue oxygen
consumption, of the electrical brain activity, and of the body temperature, either
by invasive or non-invasive devices.[2] Among the aforementioned variables, ICP measurement and its maintenance at levels < 20 mm
Hg is, alone, the most important factor for a good neurological outcome.[3]
The gold standard for the measurement and follow-up of ICP still is the use of intracranial
devices, specifically with the implantation of catheters. However, the invasive approach
of this technique has multiple disadvantages and potential severe complications, such
as bleeding and infections; moreover, it requires the presence of a specialized professional—in
this case, a neurosurgeon—that is not available in most services. In many cases, even
with the availability of a neurosurgeon, there are contraindications to the procedure,
such as bleeding disorders.[4]
In recent years, several noninvasive methods have been developed to provide an alternative
for the diagnosis of ICH, such as transcranial neuroimaging and Doppler studies.[8] However, although these methods pose less risk of complications, their accuracy
remains limited.
Ultrasonography of the optic nerve sheath (USONS) is a promising diagnostic tool that
can be used at the bedside. Since the optic nerve is a continuation of the central
nervous system, it is encased by cerebrospinal fluid (CSF). Therefore, if the circulation
of CSF is not blocked, the increased ICP is transmitted through the subarachnoid space
around the optic nerve, within its sheath, especially in the retrobulbar segment.[12]
The present article reports the utility of USONS in the diagnosis of a patient with
idiopathic intracranial hypertension (IIH).
Case Report
A male patient, 25 years old, physician, presented to the neurology clinic with a
10-day history of holocranial headache of mild to moderate intensity and of progressive
character, reported as a “headache sensation” and associated with visual changes described
as scintillating scotomas and turbidity. A general physical examination showed that
the patient was obese (body mass index [BMI] = 48 kg/m2) and presented violet abdominal striae. The ophthalmologic evaluation with retinography
evidenced inaccurate limits of the optic disc bilaterally, with poorly delimited margins
and exudates, consistent with papilledema ([Figs. 1] and [2]). There was no acuity or reduction of the visual field. The neurological examination
did not show alteration of consciousness, cranial nerve palsy or focal deficit. General
laboratory tests revealed only abnormalities in the cholesterol levels. There was
no hormonal disturbance. A magnetic resonance imaging (MRI) exam was requested for
etiological investigation and showed an empty sella and increased CSF space in the
optic nerve sheath, but no other findings. Due to the clinical suspicion of IIH, an
USONS was performed, and its result suggested ICH, with a nerve sheath of 0.52 mm
on the right side ([Fig. 3]) and of 0.54 mm on the left side (the normal reference value adopted in our service
is up to 0.48 mm).[13] A lumbar puncture was performed with the patient in left lateral decubitus which
an opening pressure of 36 mm Hg. The analysis of the CSF (cytology, cytometry, total
protein, glucose, lactate dehydrogenase, and microbiological tests for bacteria and
fungi detection) revealed normal findings, confirming the suggested diagnosis of IIH.
Treatment with acetazolamide was started at an initial dose of 750 mg/day (250 mg,
3 times per day) and, as a non-pharmacological measure, the patient was oriented to
lose weight through dieting and physical activities; in addition, he should be followed-up
by the neurological and ophthalmic services. At a new outpatient visit, 45 days post-treatment
the patient reported resolution of the headache and visual changes. An ophthalmologic
evaluation with a new retinography showed resolution of the papilledema ([Figs. 4] and [5]). The patient was under nutritional monitoring, having already lost 8 kg.
Fig. 1 Retinography—right eye—Optical disc with poorly delimited edges and exudates, consistent
with papilledema.
Fig. 2 Retinography—left eye—Optical disc with poorly delimited edges and exudates, consistent
with papilledema.
Fig. 3 Ultrasonography of the optic nerve sheath—right eye—Increased diameter of the nerve
sheath (diameter = 0.52 mm, reference value adopted at the service = up to 0.48 mm).
Fig. 4 Retinography after 45 days of treatment—right eye—optic disc with sharp edges and
no exudates.
Fig. 5 Retinography after 45 days of treatment—left eye—optic disc with sharp edges and
no exudates.
Discussion
Idiopathic intracranial hypertension is a pathology of unknown etiology that affects
mainly young, obese women. The fundamental problem in this disease is the chronic
elevation of the ICP, and its most important neurological manifestation is papilledema,
which can lead to progressive optic atrophy and blindness.[14]
The presentation of a patient with ICH symptoms (headache, visual impairment and papilledema)
should be considered a medical emergency, and a neuroimaging examination (preferably
MRI) should be performed to investigate the presence of an intracranial expansive
lesion. If detectable lesions are absent, the diagnosis of IIH is likely. This pathology
is not associated with a specific risk of mortality, but morbidity is observed as
a result of incapacitating headache and, specially, visual changes that can progress
to blindness.[15]
[16]
A study by Prunet et al showed that the normal optic nerve sheath diameter (ONSD)
ranges from 0.30 to 0.49 mm.[13] Soldatos et al showed that head trauma patients present a proper correlation between
ONSD and ICH, demonstrating that values > 0.54 mm correlate with increased ICP values
(> 20 mm Hg) with 71% sensitivity and 100% specificity.[17] Roque et al also studied the usefulness of the ONSD measurement, indicating a cutoff
diameter of 0.50 mm.[18]
Conclusion
Ultrasonography of the optic nerve sheath is a non-invasive technique, easy to perform
at the bedside, with no associated complications, that can be useful in the research
and monitoring of patients with clinical suspicion and diagnosis of IIH. It appears
as a promising procedure for the evaluation of ICP in various contexts that can coexist
with ICH.
