Keywords posterior fossa approach - pseudoaneurysm - vertebral artery - endovascular treatement
Palavras-chave acesso à fossa posterior - pseudoaneurisma - artéria vertebral - tratamento endovascular
Introduction
The vertebral artery (VA) has four segments. Segment V1 runs from the vertebral artery
origin to the C-6 transverse process. Segment V2 is the portion of the artery that
courses through the C-6 to the C-2 transverse processes. Segment V3 runs from the
C-2 transverse process to the entry in the dura mater. The segment V4, which is the
intradural portion of the artery, ends in the confluence with the basilar artery.[1 ]
[2 ]
[3 ]
[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
The V3 segment, or suboccipital segment, is in turn divided into three parts. First,
the vertical part runs between the C-1 and C-2 transverse processes and contains the
proximal loop. The second is the horizontal part, formed by the segment of the artery
that courses in the groove of the posterior arch of the atlas, and that contains the
distal loop. Third, there is the oblique part, which projects superomedially from
C-1 and enters the dura mater.[1 ]
[2 ]
[3 ]
[7 ]
The horizontal part of the V3 segment is the most exposed portion of the vertebral
artery to potential iatrogenic injuries during surgical approaches to the posterior
fossa.[3 ]
[7 ]
We present an unusual case of a patient who was operated on a giant neuroma of the
left vagus nerve, with incidental vertebral artery iatrogenic injury, the development
of a delayed giant pseudoaneurysm, and the treatment for this complication.
Case Report
A 34-year-old man with history of neurofibromatosis extending throughout the central
and peripheral nervous system had been operated on multiple spinal dorsal schwannomas
that caused cord compression. He presented with worsening of gait disturbance in a
myelopathy context due to his neurological history. Upon physical examination, the
stability of his myelopathy was verified and, instead, we found an affectation of
the 7th , 8th , 9th and 10th left cranial nerves, together with a worsening of the previous gait disturbance.
Upon cranial magnetic resonance (MR), two tumors were found. Both were located bilaterally
in the cerebellomedullary cisterns. The right tumor was small and of insignificant
size. The left tumor was very voluminous, with significant brain stem compression,
and with important extracranial extension through the jugular foramen. We suspected
the tumors were lower cranial nerves neuromas, most probably from the vagus nerve
on the left side ([Fig. 1 ]).
Fig. 1 Preoperative cranial MR. (A) Coronal view showing bilateral lower cranial nerves
neuromas located at both cerebellomedullary cisterns. The right one is very small
and insignificant in size. On the other hand, the left tumor shows significant size
and compression of the brain stem. (B) Coronal view showing compression and distortion
of the brain stem by the left vagus nerve neuroma. No hydrocephalus is apparent. (C)
Coronal view showing important extracranial extension of the left tumor through the
jugular foramen. (D) Axial view showing the left tumor at the cerebellomedullary cistern.
The tumor is multilobulated and shows significant brain stem compression.
No new spinal tumors were found upon the spinal MR.
The patient underwent surgery to achieve brain stem decompression.
We performed a lateral suboccipital retrosigmoid approach. Patient positioning was
“park bench,” and intraoperative neurophysiological monitoring was set up. During
muscular dissection, the left vertebral artery was accidentally injured in its third
portion. The hemorrhage was controlled with tamponade and hemostatic agents, and the
rest of the surgery was performed without incidents. We achieved a gross subtotal
removal of the intracranial tumor extension, obtaining satisfactory brain stem decompression.
A very little portion of the tumor was left because of its adherences to the facial
nerve and the brain stem, when intraoperative neurophysiological potentials were affected
(left 7th cranial nerve and right upper limb) ([Fig. 2B ]).
Fig. 2 Postoperative studies. (A) Immediate postoperative Angio-CT scanner performed to
rule out any complication on the vertebral artery injured during surgery. No thrombosis,
dissection, pseudoaneurysm, or any other complication develop in the immediate postoperative
period. Red arrow showing indemnity of the left vertebral artery at V3 portion. (B)
Postoperative MR showing gross subtotal removal of the intracranial portion of the
left tumor. A very small portion of the tumor had to be left because of its adherences
to the facial nerve and brain stem, when the intraoperative neurophysiological potentials
were affected. The procedure achieved satisfactory brain stem decompression and restoration
of normal anatomy. Histopathological findings confirm schwannoma. (C) Compact cellular
pattern in Antoni A fiber areas (hematoxylin-eosin stain). (D) Negativity for neurofilaments.
(E) Positivity for S100 protein.
We employed an Angio-CT scanner in the immediate post-operatory period to rule out
any complication of the injured vertebral artery. We found no thrombosis, dissection,
pseudoaneurysm, or any other complication. The CT-angiography showed indemnity of
both vertebral arteries ([Fig. 2A ]).
The postoperative course was favorable and the patient recovered from the 7th and 8th cranial nerve affectation and his gait disturbance diminished. On the other hand,
the 9th and 10th cranial nerves remained affected, and the patient was sent to rehabilitation therapy.
The pathologist reported schwannoma, confirming the presumptive diagnosis ([Figs. 2C ], [2D ], [2E ]).
Four weeks later, the patient developed a sudden painful lump with important tension
on the left retroauricular region. A CT scanner showed a soft tissue hematoma ([Fig. 3 ]). An angiogram was made and it demonstrated a giant pseudoaneurysm of the V3 portion
of the left vertebral artery ([Fig. 4 ]). The pseudoaneurysm was treated by coil embolization in the same act. The postembolization
angiogram showed exclusion of the pseudoaneurysm and permeability of the vertebral
artery ([Fig. 5 ]).
Fig. 3 A CT scanner four weeks after surgery showing a soft tissue hematoma on the left
retroauricular region as the patient develops a sudden painful lump with important
tension.
Fig. 4 An angiogram demonstrates a giant pseudoaneurysm originating from the horizontal
portion of the V3 segment of the left vertebral artery. The pseudoaneurysm is 25 × 40 mm
in size, and has a proximal and a distal lobule.
Fig. 5 Endovascular coil embolization of the pseudoaneurysm is performed. Only the proximal
lobule of the pseudoaneurysm is treated. A complete exclusion of the pseudoaneurysm
is achieved and vertebral artery permeability is maintained. Immediately after the
procedure the patient is relieved from pain. Three months after the endovascular procedure,
the patient no longer has the lump.
The postoperative course was favorable and the lump diminished in size and tension,
no longer inflicting pain on the patient.
Three months later, the patient no longer had the lump.
Two years later, the postoperative studies, MR-angiography, and Angiogram, still showed
exclusion of the pseudoaneurysm and permeability of the vertebral artery ([Fig. 6 ]).
Fig. 6 MR-Angiography two years after the embolization still shows exclusion of the pseudoaneurysm
and permeability of both vertebral arteries. Arrows show the horizontal portion of
the V3 segment of the left vertebral artery where the pseudoaneurysm developed.
Discussion
Although surgical injuries on the vertebral artery (SIVA) are rare, they can lead
to various different clinical outcomes. If the initial hemorrhage is controlled well,
the patient may remain asymptomatic (especially if the injured vertebral artery is
not dominant or the patient has good intracranial and extracranial collateral circulation).[9 ] On the other hand, surgical injuries on the vertebral artery may also lead to catastrophic
consequences when they are associated with serious complications, such as arteriovenous
fistula, late-onset hemorrhage, pseudoaneurysm, thrombosis, embolism, cerebral ischemia,
and death.[8 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ]
[15 ]
Once the injury occurs, the intraoperative treatment options are: hemostatic tamponade/compression,
microvascular repair of the injured artery, and ligation of the vertebral artery.
Direct hemostatic tamponade/compression may be an effective, quick, and easy measure.
However, several cases of delayed hemorrhage and arteriovenous fistula formation have
been reported.[16 ]
[17 ] Microvascular primary repair restores normal blood flow and minimizes the risk of
immediate or delayed ischemic complications.[16 ]
[17 ] However, it is technically demanding. Ligation of the vertebral artery is associated
with significant morbidity and mortality, such as Wallenberg's syndrome, cerebellar
infarction, cranial nerve paresis, quadriparesis, and hemiplegia.[12 ]
[18 ]
[19 ]
Immediate angiogram is recommended after surgical vertebral artery injury to detect
vascular complications and confirm adequate collateral circulation to the brain. However,
a normal angiogram after SIVA does not rule out the subsequent formation of a pseudoaneurysm,
and there have been reports of rebleeding days and even years after surgery.[20 ] In this situation, patients can be followed up with MR-angiography or CT-angiography
to evaluate the vessel situation and exclude the possibility of a growing pseudoaneurysm
formation.
Progressively, there has been greater introduction of endovascular management, such
as coil embolization, stent-assist coil embolization, and the use of stent grafts
or covered stents.[11 ]
[13 ]
[15 ]
[18 ] An ideal situation would be to be able to rely on an intraoperative angiogram and
an endovascular team for the immediate evaluation and treatment of the SIVA. However,
this is not the usually standard situation.
On a separate issue, considering that the horizontal portion of the V3 segment of
the vertebral artery is the most exposed to potential injuries during surgical approaches
to the posterior fossa, it is important to briefly comment on patient positioning
during the surgery to help avoid this serious complication. Perhaps Neurosurgery is
the surgical specialty in which patient position is one of the most critical aspects
of the surgical act itself. The case we present is a good example of this. Patient
positioning can minimize the risk of surgical injury to the horizontal portion of
the V3 segment of the VA. It is important to open up the interval between the artery
and the occipital bone with adequate neck flexion, head rotation, and dropping the
vertex of the head toward the floor. These maneuvers displace the superior surface
of the horizontal portion of the V3 segment away from the lower occiput, minimizing
the risk of arterial injury.[3 ]
[6 ]
[21 ]
[22 ]
Conclusion
The horizontal portion of the V3 segment of the vertebral artery is the most exposed
to accidental surgical injuries during surgical approaches to the posterior fossa.
Patient positioning is a matter of utmost importance in preventing potentially fatal
complications during this type of surgery.
If intraoperative vertebral artery injury occurs, initial control of bleeding may
be obtained with hemostatic tamponade. However, there is a risk of developing a growing
pseudoaneurysm leading to possibly fatal bleeding. An angiogram or CT-angiography
should be performed in such cases, although if normal, these cannot rule out delayed
formation of pseudoaneurysm.
The endovascular treatment is a good option in the management of this serious surgical
complication.
