Headache is a common complaint with a wide range of differential diagnoses. Spontaneous
intracranial hypotension (SIH) is an uncommon cause of novel onset persistent headaches,
typically one that occurs or worsens upon standing and is relieved by lying down,
and is often an underdiagnosed condition[1],[2],[3].
Intracranial hypotension has an estimated incidence of 5/100,000 and typically results
from a cerebrospinal fluid (CSF) leak, which leads to a decline in CSF volume. The
leak can be explained by structural weakness of the dura mater, associated with minimal
or no history of trauma. It is known that decrease in CSF volume, rather than CSF
pressure decrease, is the core pathogenic factor. The disease is slightly more common
in women and can occur in all age groups, with a typical age of incidence around 40
years[1],[2],[4],[5],[6],[7],[8].
Delay or failure to diagnose SIH may lead to life-threatening complications such as
dural venous sinus thrombosis, subdural hematoma and subarachnoid hemorrhage[3].
Imaging exams, particularly magnetic resonance imaging (MRI), play an important role
in detecting such abnormalities. Other complications described include bibrachial
amyotrophy, superficial siderosis, syringomyelia, cranial nerve palsies and rebound
intracranial hypertension[1],[4],[5].
We report a series of patients with SIH, some of whom had complications detected by
MRI of the brain.
METHODS
We reviewed the medical records and MRI studies of nine patients with SIH and describe
the complications observed in three of these patients, evaluated by neurologists at
the University of Campinas, São Paulo, Brazil, in 2016. The patients had given their
informed consent. All patients met previously-reported diagnostic criteria for spontaneous
spinal CSF leaks and intracranial hypotension. All of them underwent at least one
brain MRI. All radiological images were reviewed by at least one board-certified neuroradiologist.
We also reviewed the literature on possible complications of SIH.
Patient 1
A 49-year-old male truck driver, with a history of diabetes mellitus type 2 and previous tension-type headaches, reported a two-week history of headache
that started when he was carrying out his usual activities. It was a severe holocranial
headache (10/10intensity), maximum at the onset, which improved with lying down and
worsened with orthostasis/sitting up, associated with nausea, photo/phonophobia and
rotational vertigo. He also had a history of a minimal head contusion on an aluminum
plate a week before the onset of the symptoms, and took acetylsalicylic acid in the
first two days of headache, without any improvement.
Computed tomography (CT) of the brain without contrast at admission showed chronic
right and left subacute subdural hematomas, decrease in size of the ventricles and
enlargement of the pituitary. He was discharged with symptomatic treatment.
The patient came back three days later without having had pain relief. He was evaluated
by neurologists and had an MRI, which showed typical findings of SIH: subdural fluid
collections (hygromas), diffuse pachymeningeal enhancement, decrease in the size of
the ventricles, enlargement of the pituitary, and cerebral venous sinus engorgement.
There were also bilateral subdural hematomas (thickness of 1.0 cm on the left and
0.5 cm on the right), creating a discrete midline shift ([Figure 1]).
Figure 1 Coronal contrast-enhanced MR image with diffuse pachymeningeal enhancement and bilateral
subdural hematoma, showing a decrease in size of the ventricles and discrete dislocation
of centroencephalic structures.
The diagnosis of a spontaneous CSF leak was confirmed by radionuclide cisternography
(lumbosacral spontaneous dural fistula between L4-L5 on the right and bilateral L5-S1).
He was treated by clinical measures (lying down, analgesics, hydration, pure coffee
twice a day) and an epidural blood patch. A subdural hematoma drainage procedure was
performed as the symptoms did not improve. The patient was discharged with improvement
of the headache and without neurological deficits.
Patient 2
A 35-year-old unemployed man with hypertension, presented at the emergency department
with a history of three months of bilateral frontotemporal progressive headache, 7/10
intensity, which worsened with orthostasis/sitting up and was associated with nausea,
vomiting and otalgia, with slight improvement with the use of NSAIDs. He denied any
history of trauma and reported that he had stopped working because he could not sit
at work due to worsening of the headache. With the hypothesis of SIH, he underwent
a CT scan of the brain, which showed a decrease in size of the ventricles and cisterns
and a left frontoparietal laminar subdural hematoma. A few days later, he underwent
an MRI to complement the investigation, which showed a reduction in the size of the
ventricles, diffuse pachymeningeal thickening and enhancement, volumetric increase
of the pituitary, engorgement of the venous sinuses, bilateral subdural effusions
and bilateral frontotemporal laminar (thickness less than 0.5 cm) subdural hematomas
([Figure 2]).
Figure 2 Coronal T2-weighted MR image (A) showing hypointense left frontotemporal laminar
subdural hematoma; (B) Contrast-enhanced sagittal T1-weighted MR image showing diffuse
pachymeningeal thickening and enhancement, enlargement of the pituitary gland and
engorgement of the venous sinuses.
The diagnosis of spontaneous CSF leak was confirmed by neuroaxis MRI (enlargement
of the posterior epidural space with thin liquid in the epidural fat, and apparent
foci of discontinuity in the dura mater at the lower thoracic levels, notably on the
left), and radionuclide cisternography (altered CSF dynamics, without progression
of the radiotracer from the base cisterns to the cerebral convexity even after 24
hours, and thoracolumbar spontaneous dural fistulas between T8-T12 bilaterally, notably
T8-T9 on the left). He was treated with the same clinical measures as Patient 1, with
improvement, and needed an epidural blood patch. There was no need for hematoma drainage
and the patient was discharged with improvement of symptoms.
Patient 3
A 35-year-old female patient, unemployed (she was a pharmacist), with a history of
bariatric surgery, use of oral contraceptives and ex-smoker, presented at the emergency
department with a two-week history of severe (8/10) holocranial headache (in the occipital
region), with a progressive pattern and a clear correlation with the orthostatic position,
which improved with lying down. It was associated with nausea, vomiting, photophobia,
phonophobia, hypoacusis and was barely responsive to common analgesics.
An MRI was performed and showed signs of intracranial hypotension (engorgement of
the pituitary, sagging of the brain with herniation of the cerebellar tonsil, homogeneous
and diffuse pachymeningeal enhancement, posterior fossa with reduced size, diffuse
venous sinus engorgement, subdural effusions) and right transverse sinus thrombosis
([Figure 3A]). A CT angiography also confirmed the right transverse sinus thrombosis ([Figure 3B]).
Figure 3 Axial T1-weighted MRI (A) demonstrating hyperintensity in the right transverse sinus;
(B) sagittal CT angiography confirming the right transverse sinus thrombosis.
The diagnosis of a CSF leak was made by cysternography, which showed a spontaneous
dural leak at the cervical and thoracic levels, more evident between C7 and T1.
The patient's oral contraceptive was discontinued and she was discharged with anticoagulation
and significant improvement of headache after clinical treatment (lying down, hyper-hydration
and caffeine).
DISCUSSION
Headache is a common complaint with a wide range of differential diagnoses. Spontaneous
intracranial hypotension is an uncommon cause, which remains underdiagnosed and should
be considered in cases of orthostatic headache[1]
–
[5].
In this context, it is important to perform imaging of the brain, and that the radiologist
suspect the diagnosis. Tomographic examination can be used for screening, especially
in the emergency department, and ventricular collapse, descent of the cerebellar tonsils[1],[2] and even pachymeningeal enhancement can be observed if an iodinated contrast is
used. Hemorrhagic complications are easily detected in a CT and venous sinus thrombosis
can also be seen in this method. However, in general, the accuracy of MRI is much
higher than that of CT, and a complementary MRI should be performed in patients with
a high clinical suspicion, even when a CT scan does not reveal major alterations.
For example, small ventricles may not draw much attention in a young patient's CT,
and pachymeningeal enhancement areas are not as well defined as they are in the MRI.
When a CT raises suspicion of an SIH, it is also important to perform an MRI with
gadolinium, which is better able to depict typical findings and complications. Some
classic findings of SIHs seen in MRIs are diffuse pachymeningeal enhancement, decrease
in the size of the ventricles, subdural fluid collections, enlargement of the pituitary,
flattening of the pons against the clivus, cerebral venous sinus engorgement and sagging
of the brain[1],[2],[4],[5],[6],[9],[10],[11].
However, there are some pitfalls to avoid, such as the downward displacement of the
cerebellar tonsils into the spinal canal, which may mimic a Chiari malformation (pseudo-Chiari
malformation), subdural fluid collections mimicking a primary subdural hematoma, pachymeningeal
enhancement that may be mistaken for an infectious or neoplastic disease, and pituitary
hyperemia mimicking a pituitary tumor, such as an adenoma[8],[11],[12].
Complications associated with SIH are rare, but potentially serious, and early radiological
diagnosis favors proper management. Complications described include subdural hematoma,
cerebral venous and venous sinus thrombosis, bibrachial amyotrophy, superficial siderosis
and syringomyelia.[3],[4],[5] We have reviewed the literature on these conditions.
Subdural fluid collections in SIH range from simple thin hygromas to massive subdural
hematomas. Subdural fluid collections are common in SIH, occurring in about 50% of
patients. Mostly, they represent hygromas and are bilateral, thin, usually found over
the cerebral convexities, and do not cause significant mass effect[1],[2],[5],[13],[14]. However, subdural hematomas with varying degrees of mass effect (seen in Patient
1), sometimes shifting the midline, are not uncommon and have been described in about
20% of patients with SIH, this being the most common complication of this entity.
Subdural hematomas are typically bilateral but asymmetrical and the maximal thickness
usually ranges from 1 cm to 3 cm[4],[13].
The decrease of CSF volume can lead to compensatory enlargement of the subdural/subarachnoid
resulting in subdural hygromas; on the other hand, subdural hematomas are probably
caused by bleeding from enlarged veins in the subdural zone or tearing of bridging
veins[13],[14].
It is important to point out that a careful anamnesis should include risk factors
for hemorrhagic events, such as acetylsalicylic acid (seen in Patient 1) or anticoagulant
use, or history of hemophilia, which, in addition to SIH, increase the risk of these
complications.
The heterogeneous appearance and attenuation of the subdural hematoma in the imaging
indicates that recurrent bleeding within the subdural space is common in untreated
SIH. Studies on this entity have shown no significant differences in symptomatology,
age, sex or location of the CSF leak among patients with or without subdural hematomas
as a complication of SIH[13].
Resolution of subdural hygromas (and also the typical MRI imaging features of SIH)
can be demonstrated within days of successful treatment of the CSF leak. For subdural
hematomas with mass effect, however, resolution occurs more slowly and may take up
to a few months[13].
The main treatment of the collection of subdural fluid is the management of the underlying
CSF leak, almost always without the need for neurosurgical intervention. Besides,
a craniotomy may increase sagging of the brain. If subdural hematomas are evacuated
but the CSF leak is not treated, there is a high risk of persistent or recurrent subdural
hematomas[4],[13].
Cerebral venous thrombosis is found in about 2% of the population with SIH[15].
The Virchow's triad comprises three categories of factors that contribute to venous
thrombosis: venous stasis, hypercoagulability (hyperviscosity) and vessel damage[16],[17]. Spontaneous intracranial hypotension is a risk factor for cerebral venous thrombosis
according to the following mechanisms that make up the triad: venous engorgement due
to the loss of CSF (Monro-Kellie doctrine)[18] results in the slowing of venous blood flow (venous stasis); the loss of CSF reduces
absorption of CSF into the cerebral venous sinuses leading to an increase of blood
viscosity (hypercoagulability); and sinking of the brain due to the loss of buoyancy
may reflect in damage of cerebral veins and sinuses (vessel damage)[15],[19].
As previously mentioned, a thorough anamnesis is very important, and should include
other risk factors for thrombotic events, such as a previous history of thrombosis,
use of contraceptives with estrogen (seen in Patient 3), pregnancy, puerperium, and
thrombogenic disorders.
As concern imaging findings, a CT scan can show a spontaneous hyperdensity, or a T1-weighted
sequence in MRI may reveal a hyperintensity in the sinus or vein location, which represents
the thrombus. A CT or MRI angiograph may show the ‘empty delta sign’ (classically
described for sagittal sinus thrombosis) at the confluence of the sinus, or a filling
failure in the thrombosed sinus[20].
Central venous thrombosis is a serious complication, potentially life threatening,
with a patient fatality rate of up to 5% and it may also complicate a cerebral venous
infarction, which may occur in up to 40% of the patients, according to some studies.
Successful treatment combines anticoagulation and the treatment of the spinal CSF
leak[15],[19].
Bibrachial amyotrophy is characterized by weakness and atrophy of a few contiguous
cervical myotomes (segmental amyotrophy) and it is associated with an extra-arachnoid
encapsulated fluid collection that causes chronic pressure on the ventral aspect of
the cord. These extra-arachnoid fluid collections may be associated with a CSF leak.
This may be mistaken for a motor neuron disease, and sensory symptoms are minimal
or absent[4],[21].
Superficial siderosis, in the context of SIH, is a result of hemosiderin deposition
in the subpial layers of the brain and spinal cord and may be caused by repeated hemorrhage
into the subarachnoid space. This may happen due to bleeding from friable vessels
of a dural defect or due to exudation from engorged vessels (frequently seen in CSF
hypovolemia). Impaired hearing and ataxia may be seen as neurologic manifestations,
especially when the superficial siderosis occurs in the posterior fossa and cranial
nerves, and cerebellar involvement occurs[4],[21],[22].
Syringomyelia is a rare complication associated with significant downward displacement
of the cerebellar tonsils. It may vary from very small to quite extensive[4].
It is important that the radiologist identifies not only the classic imaging findings
related to SIH, but also the possible associated complications, which often influence
the clinical or surgical treatment of the patient.
