Mycotic Cerebral Aneurysm
Sidney E. Croul
University of Toronto and Toronto General Hospital
Toronto, Ontario, Canada
The patient was a 54 year old man with a history of multiple cerebral aneurysms who
in the spring of 2009 had a complex multilobated aneurysm in the left carotid circulation successfully
treated with interventional coiling. He return in the fall of 2009 and received two interventional
pipeline stents as treatment for multiple right sided internal carotid aneurysms. Five days after the
procedure, he experienced significant blood loss from the catheterization site, hypotension, and new
weakness of his left leg. He was readmitted to hospital and a subsequent CT angiogram documented a new
occlusion of his right anterior cerebral artery just distal to the pipeline stents. Workup of the right
femoral catheterization site identified an infected pseudoaneurysm which required resection. Despite
aggressive therapy, within one week CT angiography revealed both new cerebral aneurysms and intracerebral
History and Clinical findings:
This 54 year old man presented with multiple, bilateral cerebral aneurysms in the anterior
circle of Willis. In the spring of 2009, a complex multi-lobated aneurysm in the left carotid
circulation was successfully treated at Toronto Western Hospital by interventional coiling. He returned
to Toronto Western in the fall of 2009 and received two interventional pipeline stents as treatment for
multiple right sided internal carotid aneurysms. The day following that procedure, a pseudo aneurysm was
noted at his right femoral puncture site and was treated with sand bag pressure. Discharge was on the
third post-procedure day. Eight days after the procedure, he experienced significant blood loss from the
catheterization site, hypotension, and new weakness of his left leg. He was readmitted to hospital and a
subsequent CT angiogram documented a new occlusion of his right anterior cerebral artery just distal to
the pipeline stents. The right femoral pseudo aneurysm was treated with thrombin injection at
readmission. However, 14 days after the initial procedure, signs of infection were noted. These
included positive blood cultures for gram positive cocci and distal embolization. They necessitated
resection of the infected arterial segment. Nonetheless, the patient remained septic with positive blood
cultures for staphylococcus aureus on the 16th post procedure day. Despite aggressive
therapy, CT angiography on the 21st post procedure day revealed new cerebral aneurysms just
distal to the anterior cerebral artery occlusion with an associated intracerebral hemorrhage. Over the
ensuing 10 days, he became progressively hemodynamically unstable and lost brainstem reflexes. Life
support measures were withdrawn on day 31 post procedure.
The surgically resected femoral artery was invaded by an acute and chronic inflammatory
process with partial destruction of both the muscular and elastic layers. Gram stains demonstrated
groups of cocci.
At autopsy, following removal of the brain, the coils in the left supra-clinoid aneurysms and the
residual right carotid artery were visible. Examination of the circle of Willis demonstrated more of the
multi-lobated, previously coiled, aneurysm found in proximity to the left internal carotid artery.
Unfortunately, both the left and right A1 portions of the anterior cerebral artery as well as the
anterior communicating artery were fragmented beyond recognition by the initial brain removal.
The brain itself was discolored and softened. The right frontal lobe was swollen and enlarged. The
right uncus as well as the cerebellar tonsils were discolored and the left tonsil appears soft and
necrotic. Coronal sections demonstrated a zone of hemorrhage and tissue softening extending from the
base at the level of the corpus striatum into the lateral ventricle. This was contiguous with hemorrhage
within the lateral ventricle. The right frontal lobe, inferior frontal lobe and parietal cortex
contained areas with marked softening and discoloration. There was clot within the 4th ventricle. The
dorsal surface of the spinal cord was layered with a cream-colored material. An area of grey-brown
discoloration 1-2 cm in length was found in the high thoracic leptomeninges.
Microscopic examination of the clot within the two pipeline stents demonstrated minimal organization
and no signs of infection. The endothelium of the right intra-cavernous carotid artery demonstrated
modest thickening, probably due to stent placement. The medial frontal cortex from the right hemisphere
showed a healing infarction. The right superior temporal cortex demonstrated multiple microglial nodules
within cortex and superficial white matter with surrounding gemistocytic astrocytes. At the base of the
brain, there was a focus of acute inflammation in the basal ganglia intermixed with the acute hemorrhage
which penetrated the brain at that point. The surrounding tissue demonstrated severe necrosis and edema.
There was severe acute inflammation engulfing the left internal carotid system with necrosis and
dilatation of vessel walls. This inflammatory process was also found along the leptomeninges of the
cerebellum and pons and accumulated in the spinal leptomeninges. Sections of right parietal and
occipital lobes as well as left frontal and temporal lobes showed minimal pathologic changes.
Gross pathology of the other organs was unrevealing. Microscopically, foci of acute and chronic
inflammation were found in the myocardium at the base of the tricuspid and aortic valves as well as in
the renal cortices. Foci of acute and chronic pneumonia were also noted in the middle and lower lobes of
the right lung.
Final diagnosis in this case was a mycotic aneurysm of the femoral artery and a secondary mycotic
aneurysm of the circle of Willis. The cerebral mycotic aneurysm was due to septic embolization to the
region of pipeline stent placement in the right carotid artery. The right hemispheric healing
infarction, microglial nodules, and astrocytosis were felt to represent vascular events in the right
carotid circulation noted on post-procedure day eight. Meningitis reflected dissemination from the
cerebral mycotic aneurysm. Hemorrhage at the base of brain and into ventricular system was secondary to
rupture of the cerebral mycotic aneurysm.
Mycotic Cerebral Aneurysm
Features of particular interest in this case were the post angiographic femoral mycotic aneurysm and
the complications surrounding use of the pipeline stents. The majority of femoral pseudo aneurysms and
their infected kin are associated with intravenous drug abuse. However, the incidence of femoral pseudo
aneurysms following angiography has been increasing since the advent of more extended endovascular
techniques with rates a different centers ranging from 2-8%
Although infection of these
iatrogenic aneurysms is rare, our review of the literature found six reports documenting eight cases
Given the frequency of post-angiographic pseudo aneurysms, that number may grow in
Review of Literature:
A ruptured intracerebral mycotic aneurysm was described in 1869 by Church in a boy with mitral valve
described a patient with sub-acute bacterial endocarditis who at
autopsy had a ruptured aortic aneurysm secondary to "mycotic endarteritis". During that part of the 19th
century, the term "mycotic" was used to describe all microorganisms. Although the majority of these
aneurysms are due to bacteria and not fungi, the term mycotic aneurysm has persisted despite attempts to
supplant it with a more correct terminology such as infectious aneurysm .
The majority of intracranial mycotic aneurysms develop in the setting of left-sided bacterial
This suggests that these aneurysms result from the embolization
of infected material . The predominance of mycotic aneurysms in the distal middle cerebral
circulation supports this pathophysiology. This contrast with classical berry aneurysms of the brain
which have a predilection for the more proximal branch points of the circle of Willis. Because of the
primary involvement of the muscular layer, infectious aneurysms are actually pseudo-aneurysms. Multiple
aneurysms occur in up to 25% of cases
Less frequently, they develop from intracranial
bacterial infections such as meningitis, cavernous thrombophlebitis, and post-neurosurgical infections
which spread by contiguous infection to create the aneurysms
The incidence of bacterial
endocarditis over the last several decades has remained stable at two to six cases per 100 000 people per
year in the developed world. The traditional risk factor of rheumatic heart disease has been replaced by
prosthetic valves, elderly sclerotic valve disease, nosocomial hematogenous infections, and intravenous
drug use . The frequency of neurologic complications with mycotic aneurysms remains high. This is
probably because the incidence of the disease is relatively low and patients come to attention only after
neurologic signs and symptoms are reported. Although the incidence of mycotic aneurysms is reported to
be 2-4% in cases of infective endocarditis, it is probably higher due to undiagnosed cases of
Streptococcus viridans and Staphylococcus aureus are responsible for the
vast majority of mycotic aneurysms. Other bacteria implicated include coagulase-negative staphylococci,
enterococci, and beta-haemolytic streptococci. Fungi are rare causative agents
The septic embolization which usually precedes aneurysm formation is probably clinically silent in the
majority of cases. However, the most common sign is a focal neurologic deficit. In the absence of a
deficit, severe localizing headache in a patient at risk is a correlate of the embolization
Since most mycotic aneurysms are not diagnosed prior to rupture, any neurologic sign or symptom in
patients at risk should lead to diagnostic work up. CT scanning will reveal intracranial hemorrhage as
well as abscess or infarction. However, CT or MR angiography adds significant value to this evaluation
Treatment remains somewhat controversial due small numbers of patients and lack of
randomization in the literature. Noninvasive imaging modalities and minimally invasive interventional
techniques have improved the accuracy of diagnosis and expanded the therapeutic options. The most
important factor in planning treatment is whether the aneurysm has ruptured. Unruptured mycotic
aneurysms of up to 10 mm diameter have been shown to resolve on antibiotic therapy alone
Although ruptured aneurysms carry a worse prognosis, a combination of surgery and antibiotics improves
outcome over antibiotics alone
Despite the fact that interventional
techniques leave the patient with foreign material within the circulation, they have shown promise as a
treatment modality in this setting
The pipeline stent used in this patient represents a relatively new endoluminal device designed to
occlude saccular aneurysms without causing compromise or compromise of the parent artery or adjacent,
small branch arteries. The braided design is formulated to allow flow through branching vessels but to
encourage thrombosis of the trapped aneurysm . Three reports in the past year comprising the
treatment of 56 patients show excellent results
Nonetheless, it seems reasonable to
conclude that in this case the right sided infarction eight days post procedure involved the pipeline
stents and created a fertile field for the subsequent cerebral mycotic aneurysm. Experience at our
centers in Toronto is limited to 15 cases to date. The success and failure rate of this device as well
as any propensity for intravascular infectious complications will only be determined over time.
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