Transcript aneurysmal bone cysts

‫‪Middle Cerebral Artery Aneurysm‬‬
‫‪Diagnosis and Management‬‬
‫دکتر مسعود پوستی‬
‫متخصص جراحی مغز و اعصاب‬
‫بیمارستان رازی قزوین‬
ANATOMY
• The MCA is the largest and most complex of the cerebral
arteries. Some of its branches are exposed in most
operations in the supratentorial area, whether the
approach is to the cerebral convexity, parasagittal region, or
along the cranial base
• The MCA arises as the larger of the two terminal branches
of the internal carotid artery.
• Its origin is at the medial end of the sylvian fissure, lateral
to the optic chiasm, below the anterior perforated
substance, and posterior to the division of the olfactory
tract into the medial and lateral olfactory striae. From its
origin, it courses laterally below the anterior perforated
substance and parallel, but roughly 1 cm posterior, to the
sphenoid ridge.
The MCA is divided into four
segments: Ml (sphenoidal),
M2 (insular), M3 (opercular),
and M4 (cortical) . The M1
begins at the origin of the
MCA and extends laterally
within the depths of the
sylvian fissure. It courses
laterally, roughly parallel to
and approximately 1 cm
(range, 4.3–19.5 mm)
posterior to the sphenoid
ridge in the sphenoidal
compartment of the sylvian
fissure. This segment
terminates at the site of a 90degree turn, the genu,
located at the junction of the
sphenoidal and
perculoinsular compartments
of the sylvian fissure.
The perforating branches of the MCA enter
the anterior perforated substance and are
called the lenticulostriate arteries . There is
an average of 10 (range, 1–21)
lenticulostriate arteries per hemisphere
(36). Lenticulostriate branches arise from
the prebifurcation part of the M1 in every
case and from the postbifurcation part of
the M1 segment in half of the hemispheres.
The branches of the middle cerebral artery
are important for surgical orientation,
treatment paradigms and implications, and
salvage techniques. The M1 has multiple
lenticulostriate arteries that are divided into
two groups. The medial lenticulostriate
arteries enter the anterior perforating
substance superiorly and supply the
lentiform nucleus, the caudate, and the
internal capsule. The lateral lenticulostriate
arteries are more variable in their
location,traverse the basal ganglia, and
supply the caudate nucleus
Middle Cerebral Artery
Aneurysms
• The middle cerebral artery is one of the most
common sites of saccular aneurysms. They
most commonly arise at the level of the first
major bifurcation or trifurcation of the artery.
The angulation with which the bifurcating
trunks arise from the main trunk forms the
turn or curve. These aneurysms usually point
laterally in the direction of the long axis of the
prebifurcation segment of the main trunk.
Middle cerebral aneurysms
. A, scalp incision and
craniotomy for approaching aneurysms
arising on the middle cerebral
artery. B, operative view provided
by a right frontotemporal
craniotomy. The right sylvian fissure
has been split to provide this
view of the optic nerves and the
carotid and middle and anterior
cerebral arteries. Brain spatulas are
on the temporal and frontal lobes.
C, middle cerebral aneurysms are
usually located at the bifurcation
near the genu of the artery. The
arrows show the direction of
hemodynamic force at the aneurysm
site. The medial, intermediate,
and lateral lenticulostriate
arteries arise from the middle cerebral
artery. D, aneurysm arising
on an early bifurcation. E, aneurysm
arising at a large lenticulostriate
branch. F, aneurysm arising
at an early branch. A., arteries,
artery; A.C.A., anterior cerebral
artery; C.A., internal cerebral
artery; Fr., frontal; Int., intermediate;
Lat., lateral; Len.Str., lenticulostriate;
M.C.A., middle cerebral
artery; Med., medial; O.N., optic
nerve; Temp., temporal.
CLASSIFICATION OF MIDDLE
CEREBRAL ARTERY ANEURYSMS
• MCA aneurysms can be classified in many
ways, including by morphology, location,
etiology, and size.
Classification by Morphology
• Saccular aneurysms are the most commonly
encountered, followed by fusiform aneurysms.
• Extremely dysmorphic or distal aneurysms are
usually infectious and are classically identified
on distal M4 branches.
Classification by Location
• Bifurcation and trifurcation aneurysms represent up to 90% of all
MCA aneurysms and are the lesions most uniformly referred for
surgical consideration.
• Aneurysms of the Ml segment are second in frequency to
bifurcation aneurysms and are composed of lenticulostriate or
anterior temporal artery saccular aneurysms.In patients with
multiple intracranial aneurysms, the frequency of proximal MCA
aneurysms tends to increase, and nearly three fourths of patients
with multiple intracranial aneurysms harbor an MCA aneurysm.
• Rinne and colleagues examined 561patients with MCA aneurysms
and found that 39% of patients with MCA aneurysms had multiple
intracranial aneurysms, significantly higher than the 20% classically
quoted for other parts of the intracranial circulation.additionally,
these investigators found that the multiplicity of aneurysms
increased the risk for poor outcome.
Classification by Etiology
•
Saccular
•
With regard to etiology, the precise pathogenesis of the common saccular (or berry) aneurysm is incompletely understood.
These aneurysms classically form at sites of arterial curves or branching. Hemodynamic forces are likely to be an important
contributing factor in the forced segmentation of the arterial elastic membrane, which may be an important factor in the
aneurysm formation cascade.
•
Fusiform Aneurysms
•
Fusiform lesions are most frequently seen in the posterior circulation and have far different management than saccular
aneurysms . Although rare, there is no doubt that they represent a different disease process than saccular aneurysms, and in
the MCA distribution, they can grow quite large, incorporating multiple branch vessels. MCA fusiform aneurysms can be
found in all segments of the artery although classically they are found at the bifurcation.
•
Infectious Aneurysms
•
Infectious or mycotic aneurysms are most commonly found along the distal branches of the cerebral arteries.They are
typically secondary to infectious emboli, With subsequent aneurysm formation. Usually, bacterial endocarditis (65%) is
implicated in infectious aneurysms, but other idiopathic bacterial or fungal source have been implicated. Other embolic
sources include neoplastic disease, such as choriocarcinoma and atrial myxoma.
•
Dissecting Aneurysms
•
•
Dissecting MCA aneurysms are rare and may be associated with infection, connective tissue diseases such as Marfan's
syndrome, cystic medial degeneration, and fibromuscular dypslasia.
congenital weakness of the vessel wall with rupture of the elastic interna.
•
Traumatic Aneurysms
•
Traumatic aneurysms are uncommon and are most often associated with the ACA and its branches because of its proximity
to both the skull base and the faLx.Traumatic MCA aneurysms are unusual, are most classically associated with a skull
fracture, and have a high rupture rate. These lesions are most frequently distal on M3 and M4 segments and often present
Witlh delayed rupture (average, 4.7 days) after tlh inciting trauma.Classically, these are managed with surgical trapping and
excision with or without bypass.
Classification by Size
• Small(<5mm), medium (5 to 10 mm), large (11 to
25 mm), and giant (>25 mm).Most M1lenticulostriate aneurysms are quite small (which
often precludes endovascular treatment).
• Cerebral aneurysms that reach large (>15 mm) or
giant (>25 mm) size are more frequently seen in
the MCA distribution than in other arterial
distributions and can represent up to 9% of MCA
aneurysms.
PRESENTATION AND EVALUATION OF
MCA ANEURYSMS
• SAH or ICH is the most common presentation of MCA aneurysms. Because
of their propensity to become quite large before detection, they may
occasionally become symptomatic without SAH. Giant aneurysms are
reported to cause seizures more often than smaller ones, and this may be
due to mass effect, ischemic changes, or repeated subclinical
hemorrhages.
• Evaluation and treatment of patients With aneurysms varies depending on
whether an aneurysm has ruptured or not. Nonruptured aneurysms are
increasingly being discovered incidentally because of the frequency of use
of screening studies (CT, CTA,MRA) in the evaluation of any number of
unrelated symptoms.
• In symptomatic cases, CT usually reveals the presence of SAH however, a
lack of blood necessitates a LP if the history is suggestive of an aneurysm
rupture.In patients with SAH on CT or LP, we typically perform a cerebral
angiogram, with three-dimensional reconstruction of any pathology if
possible.
Basic surgical principles
•
•
•
•
•
•
•
•
•
•
1.Proximal control: The parent artery should be exposed proximal to the aneurysm. This allows control of flow to the
aneurysm if it ruptures during dissection
Exposure of the ICA above the cavernous sinus will give proximal control for aneurysms arising at the level of the
Post.Com or Ant.choroidal A.
The supraclinoid carotid or the preaneurysmal trunks of the MCA or ACA should also be exposed initially to obtain
proximal control of MCA and ACA aneurysms.
2.Exposure rule : If possible, the side of the parent vessel away from or opposite to the site on which the aneurysm arises
should be exposed before dissecting the neck of the aneurysm. The dissection can then be carried around the wall of the
parent vessel to the origin of the aneurysm.
3.Neck before fundus: The aneurysmal neck should be dissected before the fundus. The neck is the area that can tolerate
the greatest manipulation, has the least tendency to rupture, and is to be clipped.But unfortunately the origin of parent A.
trunk and perforating vessels make this difficult .So The dissection should not be started at the dome, because this is the
area most likely to rupture before or during surgery.
4. Separating and preserving of all perforating arterial branches: Separating the perforators, if tightly packed against or
adherent to the aneurysm may be facilitated by lowering the blood pressure or by temporary clipping of the parent artery.
5.Bleeding: If rupture occurs during microdissection, bleeding should be controlled by applying a small cotton pledget to the
bleeding point and concomitantly reducing mean arterial pressure. If this technique does not stop the hemorrhage,
temporary occlusion with a clip or occluding balloon can be applied to the proximal blood supply, but only for a brief time.
6. The bone flap should be placed as low as possible to minimize the need for retraction of the brain in reaching the area
7.After clipping:After the clip is applied, the area should always be inspected, sometimes with intraoperative angiography, to
make certain the clip does not kink or obstruct a major vessel and that no perforating branches are included in it
8.Broad neck base: If an aneurysm has a broad-based neck that will not easily accept the clip, the neck may be reduced by
bipolar coagulation. Nearby perforating arteries are protected with a cottonoid sponge during coagulation.