Key-words:
Angiography - basilar artery kink - brain herniation - brain sag - cerebrospinal fluid
hypovolemia
Introduction
Intracranial hypotension or brain sag can lead to classically identifiable symptoms
such as positional headaches, nausea, vomiting, and occasionally blurred vision [[Table 1]]. However, severe cerebrospinal fluid (CSF) hypovolemia can lead to a life-threatening
condition that can mimic intracranial hypertension such as transtentorial herniation
and poor neurologic exam.[[1]] In this case report, we present a case of severe intracranial hypotension from
a thoracic tumor resection leading to red herring symptoms of intracranial hypertension.
Ultimately, the pathology was proven to be CSF hypovolemia from an occult durotomy
resulting in a CSF leak. We discuss the implications of this diagnosis and how to
avoid misdiagnosis. In addition, we present a rare but well-reported finding of basilar
artery kinking in the setting of severe intracranial hypotension which dramatically
improved after durotomy repair.
Table 1: Common clinical and radiographic signs of cerebrospinal fluid (CSF) hypovolemia
Case Report
A 47-year-old female with neurofibromatosis Type 2, bilateral acoustic neuromas, deafness,
multiple intracranial tumors requiring resection, and focal epilepsy presented with
urinary incontinence and gait/balance difficulty. On work up the patient was found
to have a T3 intradural extramedullary mass [[Figure 1]], L4-5 spondylolisthesis, and a stable C4-5 disc herniation. The patient underwent
thoracic laminectomies at T3 and T4 for the resection of her thoracic mass. The immediate
postoperative course was complicated by transient right lower extremity weakness,
which subsequently returned to preoperative baseline, and the patient was discharged
to an inpatient rehabilitation facility on postoperative day 4.
Figure 1: (A) Pre-op contrast enhanced thoracic T1 and T2 weighted MRI of the T3 intradural
extra medullary mass. (B) Post resection contrast enhanced (C) T1 and (D) T2 weighted
MRI showing gross total resection
On postoperative day 9, inpatient rehabilitation staff found the patient to be experiencing
nausea, vomiting, and decreased consciousness. Computed tomography (CT) head demonstrated
acute downward herniation with cisternal effacement, including suprasellar, interpeduncular,
and crural cisterns, however not ambient or quadrigeminal cisterns [[Figure 2]]A and [[Figure 2]]B. On arrival to our institution, the patient was obtunded and intubated for airway
protection. Urgent magnetic resonance imaging (MRI) of the brain demonstrated diffuse
pachymeningeal enhancement and significant deformation of the brain stem [[Figure 2]]C and [[Figure 2]]D. This imaging in conjunction with her clinical presentation raised some concern
for possible intracranial hypertension. Despite this a central line was placed to
provide hypertonic saline, which was complicated by inadvertent injury to the right
vertebral artery. After further review, discussion of a potential durotomy from her
recent thoracic surgery raised serious consideration for an occult CSF leak and resultant
intracranial hypotension. Placement of the patient in Trendelenburg position showed
immediate clinical improvement. Expectedly, the patient would decline neurologically
when the head of bed was elevated. An angiogram was performed to evaluate the iatrogenic
vertebral artery injury encountered during central line placement, and ultimately
the right vertebral artery was sacrificed to allow for safe catheter removal. Incidentally
this angiogram revealed significant kinking of the basilar artery [[Figure 3]]B. Based on clinical concern for CSF hypovolemia, further supported by kinking of
the basilar artery, a CT thoracic myelogram was performed, which did in fact show
a CSF leak at the prior thoracic surgery site [[Figure 4]]. Subsequently, the patient underwent exploration of the thoracic wound, and a ventral
durotomy was found and repaired. Two small artificial dural patches were placed laterally
and ventrally to the thoracic cord at the level of the durotomy. Following this repair,
the patient was able to once again tolerate sitting up, with eventual recovery back
to her neurologic baseline. CT Angiography (CTA) head and neck was obtained prior
to discharge which showed interval improvement of the basilar kink with resolution
of her CSF hypotension [[Figure 3]]A and [[Figure 3]]C.
Figure 2: CT head without contrast (A) axial and (B) sagittal slices demonstrating downward
herniation with effaced cisterns concerning for acute intracranial hypotension. MRI
brain (C) contrasted T1 coronal slice demonstrating diffuse pachymeningeal enhancement,
and (D) non-contrast T1 sagittal slice again demonstrating downward herniation with
significant deformation of the brain stem. Imaging findings support concern for intracranial
hypotension contributing to clinical presentation
Figure 3: CT angiography (CTA) with (A) cerebrospinal fluid hypotension and (C) after cerebrospinal
fluid leak repair. (B) Diagnostic cerebral angiogram (DCA) demonstrating profound
basilar kinking with concurrent cerebrospinal fluid hypotension
Figure 4: CT myelogram of the cervical and upper thoracic spine (A) sagittal and (B) axial
slices revealing ventral contrast extravasation concerning for occult durotomy and
cerebrospinal fluid leak
Discussion
Intracranial hypotension, or “brain sag,” leading to extreme changes in neurological
exam remains an uncommon occurrence even after intradural neurosurgical procedures.
The well-known signs easily recognizable as indicative of intracranial hypotension
are postural headaches in addition to occasional nausea, emesis, photophobia, and
blurry vision. These signs are related to a decrease in the already negative CSF vertex
pressure in the erect posture.[[1]] The headache easily resolves with the placement of the patient in a recumbent position
and proceeding with a blood patch or CSF leak repair usually results in a permanent
cure. It is the loss of overall CSF volume with resultant brain sag and pressure on
pain-sensitive structures (located in the dura?) that leads to postural headaches
and the radiologic findings that have been well described in the literature.[[2]] These findings include subdural hematoma, pachymeningeal enhancement, cerebellar
tonsillar herniation, tentorial herniation of the splenium and cingulate gyrus, and
midbrain sagging.[[1]],[[2]],[[3]],[[4]],[[5]],[[6]],[[7]] Komotar, et al.,[[8]] described the radiologic findings deemed important in the diagnosis of brain sag
as well as clinical signs of transtentorial herniation including CT head revealing
effacement of the basal cisterns with an oblong brainstem, and improvement of symptoms
after placement of the patient in the Trendelenburg position. Although CSF hypovolemia
is known to lead to intracranial hypotension, there have been reports of patients
with spontaneous intracranial hypotension syndrome with normal CSF pressures.[[1]],[[9]] Brain sagging leading to poor neurologic exams in aneurysmal subarachnoid hemorrhage
patients has been well described in patients who underwent preoperative placement
of lumbar drains leading to significant drainage of CSF intraoperatively.[[8]] Factors such as longer surgery time and global cerebral edema on admission cranial
imaging are risk factors for brain sag after aneurysm surgery.[[8]] There have also been reports of brain sag after subdural hematoma evacuation.[[6]] Similar to the case presented here, patients present with symptoms of transtentorial
herniation including lethargy, unilateral blown pupil, and poor motor exam. The importance
of recognizing and differentiating CSF hypovolemia from true increased intracranial
pressure (ICP) cannot be overemphasized as the management algorithms are vastly different.
Patients with brain sag, or CSF hypovolemia, will improve with placement of the patient
in the Trendelenburg position. Our patient presented here arrived overnight with a
very poor neurologic exam. The patient's symptoms were not immediately recognized
as relating to CSF hypovolemia, and the patient was initially treated for refractory
high ICPs. When the patient did not improve with these interventions, the consideration
for occult CSF leak was discussed, and the patient was immediately placed in Trendelenburg
position with resulting improvement in the neurologic exam within minutes. Unlike
most reports of brain sag/CSF hypovolemia presenting 1–4 days postoperatively, the
patient described here presented in an unusually delayed manner 10 days postoperatively.
We attribute this delayed presentation to a slower flow CSF leak. Given this patient's
history being confounded by neurofibromatosis and multiple significant intracranial
lesions, the presentation was a red herring for the patient's true pathology. Ultimately
an ICP monitor was placed and confirmed normal ICPs.
Furthermore, given the iatrogenic vertebral artery injury, we were able to uniquely
obtain a cerebral angiogram of the patient's brain while in this condition. The angiographic
findings of brain sag have been well described in the literature. Alaraj, et al.,[[2]] described five patients who presented in extremis from brain sag after clipping
of the patient's aneurysm with the preoperative placement of a lumbar drain. These
patients were described as having downward displacement of the basilar artery that
was severe enough to cause basilar kinking, coined the “cobra sign” on cerebral angiogram.
These findings were described as similar to those seen in transtentorial herniation
with the exception of the presence of a mass lesion.
If unrecognized, brain sag can theoretically lead to worsening kinking of the basilar
artery and posterior circulation vasculature with resulting brain stem ischemia and
permanent neurologic deficits. If recognized and treated, Komotar, et al.[[8]],[[10]] showed that there is no difference in morbidity or mortality at discharge or at
3-month follow-up. Low ICPs and improvement in our patient's exam in Trendelenburg
position verified the diagnosis of intracranial hypotension/brain sag. Once the diagnosis
was made, steps were obtained to identify and treat the offending culprit, ultimately
an occult CSF leak after thoracic intradural surgery.
Conclusion
Mild intracranial hypotension continues to be a common finding in patients who undergo
procedures that require CSF diversion or CSF loss. Symptoms are easily recognizable
including classic postural headaches. However, more severe cases of CSF hypovolemia
can be misdiagnosed as intracranial hypertension given overlapping presenting symptoms
that can act as a red herring. It is of paramount importance for the clinician to
be aware of this diagnostic conundrum and evaluate both potential diagnoses fully
as the treatment algorithms are vastly different.
