Results from resection of cerebellopontine angle (CPA) tumors are significantly affected
by variations in adjacent neurovascular anatomy.[1]
[2] Despite an overall improvement in patient outcomes, vascular complications continue
to be reported in up to 7% of patients undergoing CPA tumor resection.[3] Due to the significant potential morbidity and mortality associated with vascular
injury, meticulous surgical technique is required to remove the tumor while minimizing
trauma to adjacent vasculature.
Vascular damage can result in acute hemorrhagic or ischemic complications. Injury
to the transverse and sigmoid sinuses may lead to thrombosis. Due to venous redundancy,
unilateral dural sinus occlusion may remain asymptomatic, although complications of
venous insufficiency can occur.[4]
In the acute setting, venous occlusion can cause cerebral edema, brain herniation,
and death, whereas more indolent chronic venous insufficiency may result in increased
intracranial pressure and the clinical syndrome of pseudotumor cerebri. Dural sinus
thrombosis is also considered a potential precursor to the development of a dural
arteriovenous fistula (DAVF), a rare vascular complication of CPA surgery.[5] We present two cases in which a DAVF developed as the result of sigmoid sinus thrombosis
following translabyrinthine tumor resection.
CASE 1
CASE 1
A 46-year-old woman presented with left-sided tinnitus and severe to profound hearing
loss. Magnetic resonance imaging (MRI) showed an enhancing 23 × 23 × 21-mm left-sided
CPA mass consistent with vestibular schwannoma (VS; Fig. [1]). Vascular anatomy appeared normal, and there was no history of coagulopathy.
Figure 1 Patient 1: Preoperative magnetic resonance image. An axial T1-weighted image with
contrast shows a classic expansile internal auditory canal and cerebellopontine angle
mass consistent with left vestibular schwannoma. No vascular abnormalities are appreciated.
A translabyrinthine resection of the VS was performed. The sigmoid sinus was exposed
in a routine manner and gently retracted with a self-retaining ribbon retractor. There
was no apparent intraoperative vascular injury.
Postoperatively, the patient experienced persistent headache, head pressure, and balance
difficulties consistent with a peripheral deafferentation vestibulopathy. There were
no signs of central vestibular dysfunction. Follow-up MRI scans at 3 and 12 months
postoperatively were interpreted as showing expected postresection changes without
explanation for the patient's persistent symptoms (Fig. [2]). Though no gross hydrocephalus was present on imaging studies, mild hydrocephalus
was considered to be a potential etiology of her symptoms, and a ventriculoperitoneal
(VP) shunt was placed. After placement of the VP shunt, the patient's headache and
balance difficulties improved significantly.
Figure 2 Patient 1: Magnetic resonance image acquired at 1 year postresection. An axial fast
spin echo T2-weighted image shows multiple serpiginous hypointense structures (white
arrows) consistent with venous flow voids in the basal cisterns and overlying the
cerebral hemispheres. These were not noted prospectively but are definitely abnormal
and represent abnormally dilated and tortuous cortical veins.
An MRI 2 years postresection and 2 months post-VP shunt showed striking enlargement
and tortuosity of cortical veins in the middle and posterior cranial fossae (Fig.
[3]). Abnormal serpentine flow voids were seen in the basal cisterns and overlying the
cerebellar hemispheres and temporal lobes, strongly suggestive of a DAVF.
Figure 3 Patient 1: Magnetic resonance image acquired at 2 years postresection. An axial T2-weighted
image shows marked interval progression of abnormal serpiginous vessels consistent
with dilated veins in the basal cisterns and overlying the cerebellar hemispheres
and temporal lobes (white arrows). This image was acquired after the patient received
a ventriculoperitoneal shunt. S, susceptibility artifact due to shunt hardware.
Cerebral angiography confirmed the diagnosis of a left transverse sinus DAVF fed by
multiple external carotid and internal carotid branches (Fig. [4]). The most prominent arterial feeders included the occipital and posterior meningeal
arteries bilaterally and the left meningohypophyseal trunk. The left transverse sinus,
sigmoid sinus, and internal jugular vein were occluded, with retrograde flow into
the cortical veins and right sigmoid sinus, as well as globally delayed venous drainage.
Figure 4 Patient 1: A catheter angiogram at 2 years postresection. (A) A lateral view from
a left external carotid artery (ECA) injection demonstrates an abnormally enlarged
occipital artery (white arrows) and abnormally enlarged posterior meningeal artery
(black arrows). Multiple smaller serpentine-like vessels are seen converging on the
distally occluded left transverse sinus (*). These vessels constitute ECA feeders
of the dural arteriovenous fistula (DAVF). (B) A lateral view from a left internal
carotid artery (ICA) injection demonstrates an abnormally enlarged and irregular meningohypophyseal
trunk (black arrows) feeding the fistula (*). (C) An anteroposterior view from a later
time (venous phase) in the left ICA injection demonstrates a tangle of vessels in
the region of the distal left transverse sinus (L trv), consistent with extensive
cortical venous drainage of the DAVF. There is also distal occlusion of the left transverse
sinus (white arrow). Opacified blood in the left transverse sinus drains across the
torcular herophili into the right transverse sinus (R trv), and then to the right
sigmoid sinus and internal jugular vein.
Transvenous coil embolization obliterated the fistula. The patient did well initially,
but experienced severe headaches 3 months later. A diagnostic cerebral angiogram showed
interval development of a new DAVF, adjacent to the previously embolized fistula and
fed by the middle meningeal artery. Transarterial embolization of the middle meningeal
artery resulted in fistula obliteration. The patient's symptoms improved, and a recent
angiogram obtained more than 2 years following the initial embolization shows no evidence
of recurrence of either fistula.
CASE 2
CASE 2
A 67-year-old man presented with a 20-year history of progressive left hearing loss,
progressing to complete deafness over the past 3 years. He had no other neurological
symptoms or signs. MRI showed a 26 × 35 × 43-mm homogeneously enhancing, dural-based
mass arising from the posterior petrous face with extension into the left internal
auditory canal, consistent with meningioma (Fig. [5]). There was moderate compression of the brain stem, but no obstructive hydrocephalus.
The preoperative MRI was otherwise negative, with no evidence of a vascular malformation.
Figure 5 Patient 2: Preoperative magnetic resonance image. A coronal T1-weighted image with
contrast shows a homogeneously enhancing left cerebellopontine angle mass, extending
into but not enlarging the left internal carotid artery, consistent with a petrous
meningioma. There are no vascular abnormalities present.
Translabyrinthine resection was performed. The sigmoid sinus was widely exposed and
gentle retraction of the sigmoid sinus and posterior fossa dura was performed. A small
laceration of the sinus was repaired with 6–0 prolene sutures prior to closure.
A follow-up MRI acquired 2 years postresection showed bilateral tortuous, corkscrew-like
flow voids consistent with venous collaterals over the cerebral convexities and traversing
the basilar cisterns (Fig. [6]). There was an absence of flow void in the left transverse and sigmoid sinuses.
A DAVF was suspected, but because the patient was asymptomatic, he declined angiography
until a follow-up MRI 6 months later demonstrated progression of abnormal cortical
venous drainage (Fig. [7]).
Figure 6 Patient 2: Magnetic resonance image acquired at 2 years postresection. (A) An axial
fast spin echo (FSE) T2-weighted image shows abnormally prominent, dilated, and tortuous
cortical veins overlying the cerebellar and cerebral hemispheres, as well as present
in the basal cisterns (white arrows). (B) A more superior axial FSE T2-weighted image
from the same study show abnormally numerous, tortuous, and dilated veins more superiorly
at the base of the brain, in the sylvian fissures, and overlying the cerebral hemispheres
(white arrows). This finding was interpreted as strongly suggestive of dural arteriovenous
fistula, but the patient initially refused angiographic evaluation.
Figure 7 Patient 2: Magnetic resonance image acquired at 2.5 years postresection. An axial
fast spin echo T2-weighted image shows progression of abnormal veins, with a marked
increase in caliber and tortuosity. This is particularly evident around the cerebral
peduncles and in the interpeduncular fossa (white arrows).
Cerebral angiography confirmed the diagnosis of a left transverse sinus DAVF that
was supplied by multiple branches of the left external carotid artery (Fig. [8]). The most prominent contributions came from the occipital, ascending pharyngeal,
and middle meningeal arteries, with minor contributions from the left meningohypophyseal
trunk, inferolateral trunk, and right occipital and middle meningeal arteries. The
left transverse sinus, sigmoid sinus, and jugular vein were occluded. There was retrograde
flow into cortical veins, superior sagittal sinus, and contralateral sigmoid sinus,
with delayed venous drainage globally.
Figure 8 Patient 2: Catheter angiogram. Selective angiogram of the left external carotid artery
in lateral (A) and anteroposterior (B) projections. (A) Late venous phase of an external
carotid artery (ECA) injection. The left sigmoid sinus is occluded at the transverse-sigmoid
junction, multiple dilated cortical veins are present, and dural sinus venous egress
is in a retrograde fashion via the right transverse sigmoid sinus. (B) Arterial phase
of an ECA injections demonstrate dural arteriovenous fistula at the left transverse
sigmoid sinus junction, with feeders from prominent transosseous branches of the occipital
artery, middle meningeal artery, and posterior auricular artery.
Partial arterial and venous embolization was attempted, with persistence of the fistula
on angiography. Therefore, a combined surgical-endovascular approach was undertaken.
A left occipital-suboccipital craniotomy was used to provide access to the left transverse
sinus and endovascular coils were deployed, with additional coil embolization of the
occipital artery. Follow-up MRI demonstrated marked regression of the DAVF, but an
angiogram 6 months postembolization demonstrated fistula recurrence, and further intervention
is planned.
DISCUSSION
DISCUSSION
DAVFs were rarely identified before 1960. In the 1970s, these lesions were increasingly
reported due to advances in angiography.[6] A DAVF is defined as an artery-to-vein shunt in the dura mater without a discrete
nidus or an intervening capillary bed. DAVF is also a dynamic process. In the early
stages, venous outflow may be relatively unobstructed, but progression over time may
result in retrograde flow and eventually cortical venous drainage.[7] This results in elevated venous pressures, with attendant risk of intracranial hemorrhage
and other complications of venous hypertension.
DAVFs vary greatly in size, location, and drainage patterns, and hence their clinical
presentation is highly variable. They may be asymptomatic or may cause pulsatile tinnitus,
ocular symptoms, headache, vertigo, seizures, focal neurological deficits, increased
intracranial pressure, or hemorrhage. DAVF involving the transverse and sigmoid sinuses
is the most common type encountered by the neurotologist, as these patients often
present with pulsatile tinnitus.[7] Although one of our patients reported nonspecific symptoms of headache, pressure
sensation, and balance difficulties, the other was surprisingly asymptomatic despite
extensive and progressive cortical venous drainage.
Several postulations exist regarding the pathogenesis of DAVFs. They may be congenital
or acquired, but most are acquired, often in association with venous sinus thrombosis.
A hypercoagulable state, vascular manipulation, and/or trauma are potential triggers.[8] Several hypotheses have been suggested to explain the development of postsurgical
DAVFs. Sakaki et al presented a series of five postsurgical dural fistulae, in which
histopathologic examinations of resected DAVFs showed subintimal fibrous thickening
and hypertrophy of the sinus wall, as well as numerous intramural dural vessels.[9] Thrombus was seen in only two of five cases. It was suggested that sigmoid sinus
sacrifice resulted in intrasinus hypertension, which then induced DAVF formation.
Concurrent arterial and venous injury during craniotomy may also result in DAVF.[10] Desal et al suggested that venous disruption may induce angiogenesis and create
an arteriovenous shunt in the dural sinus wall.[11]
The transverse and sigmoid sinuses are at particular risk in neurotologic surgery.
Occlusion may be intentional or may result from mechanical, thermal, compressive,
or desiccation injury.[12] Given the routine manipulation of the sigmoid sinus during translabyrinthine approaches,
it is somewhat surprising that DAVFs are not more common. A search of the medical
literature revealed a similar report of this complication identified 2 years following
VS resection.[10] Sakaki et al reported five cases of DAVF that developed in the transverse-sigmoid
sinus after surgical resection of the sigmoid sinus during tumor removal, but none
of the cases reported involved CPA surgery or resulted from sinus retraction alone.[9]
Our patients had no identifiable predisposing risk factors that would have predicted
the development of DAVF. One had nonspecific symptoms, and the other was asymptomatic.
Classic pulsatile tinnitus was absent, presumably related to preexisting hearing loss.
Initial imaging findings were subtle and were only detected as the process evolved
on follow-up imaging studies. This highlights the fact that the diagnosis of DAVF
can be somewhat difficult to make on cross-sectional imaging studies, and the treating
clinician and interpreting radiologist must have a high index of suspicion to make
this diagnosis. This is especially true in the setting of prior posterior fossa surgery
where venous sinuses may have been injured and thrombosed.
Digital subtraction catheter angiography is generally necessary to confirm the diagnosis
of DAVF. Computed tomography (CT) and MRI lack sensitivity in detection of DAVFs,
though recent advances in magnetic resonance and CT angiography have improved the
noninvasive diagnosis of this entity. In a review of 46 patients with DAVF diagnosed
between 1990 and 2006, Cohen et al reported that CT angiography had a sensitivity
of 15.4% and MR angiography had a sensitivity of 50% compared with conventional angiography.[13] Catheter angiography should therefore be performed when there is high clinical suspicion
for a DAVF, even if CT or MRI is interpreted as normal.
Endovascular therapy with embolization is the initial treatment of choice for symptomatic
and progressive DAVFs involving the sigmoid or transverse sinus.[14] Our cases suggest that although this can be curative, ongoing clinical and imaging
vigilance is needed given the potential for these lesions to recur.
CONCLUSION
CONCLUSION
DAVF is an uncommon complication of CPA surgery. Difficulty in diagnosis may occur
because of nonspecific presenting symptoms and subtle findings on routine postoperative
imaging studies, and the potential lack of pulsatile tinnitus. Cerebral angiography
is the gold standard for diagnosis, and endovascular occlusion is usually the treatment
of choice. Because of the potential for considerable morbidity, every effort should
be made to minimize injury to the dural sinuses during skull base surgery.
