Shinshu Med J, 71⑹：415～422, 2023

Mycotic Posterior Inferior Cerebellar Artery Aneurysm Following
Meningitis after Endoscopic Endonasal Transsphenoidal Surgery :Case Report and Review of the Literature
Francis Campbell1）2）, Toshihiro Ogiwara1）＊, Daishiro Abe1）, Yu Fujii1）, Akifumi Yokota1）
Akihiro Chiba1）, Takaaki Kamijo1）, Yoshiki Hanaoka1）, Ridzky Firmansyah Hardian1）
Samuel Chukwunoyerem Ohaegbulam2） and Tetsuyoshi Horiuchi1）1） Department of Neurosurgery, Shinshu University School of Medicine
2） Unit of Neurosurgery, Memfys Hospital for Neurosurgery, Enugu, Nigeria

Mycotic intracranial aneurysms (MIAs) are rare infection-mediated arterial wall destructions that result in
focal vessel weakness and dilatation. They commonly involve the anterior cerebral circulation, usually following
hematogenous embolization from infective cardiac vegetation, and are associated with an elevated risk of rupture.
MIAs arising from a posterior inferior cerebellar artery (PICA) are uncommon, and those resulting from contig­
uous infections are extremely rare. Here, we present a case report and review the literature on rare MIAs in­volving the distal PICA segment following meningitis after endoscopic endonasal transsphenoidal surgery. A
75-year-old man presented with a 2-year history of progressive visual impairment of the left eye, for which
initial cranial magnetic resonance imaging suggested optic perineuritis ; however, conservative managementwith high-dose steroid therapy did not improve the patient’s condition. He subsequently had biopsy, which con­firmed an optic nerve sheath meningioma, for which optic nerve decompression via the endoscopic endonasal
approach (EEA) and follow-up radiation therapy was done. He developed postoperative meningitis and subse­
quently had rupture of left PICA mycotic aneurysm (angiography done a month earlier demonstrated normal
left PICA). Risk factors for meningitis were invasive cranial intervention, prolonged steroid use, and radiation
therapy. Coil embolization was successfully performed ; however, the patient succumbed to irreversible hernia­
tion and infection. MIAs arising from the PICA following meningitis are rare, but complications following surgi­
cal intervention and rupture are associated with high morbidity and mortality. A high index of suspicion andearly intervention before rupture may prevent poor outcomes. Shinshu Med J 71 : 415―422, 2023
(Received for publication June 30, 2023 ; accepted in revised form August 21, 2023)
Key words : mycotic intracranial aneurysm, endoscopic endonasal surgery, subarachnoid haemorrhage,
coil embolization, meningitis

Ⅰ Introduction

other microbes from infective cardiac vegetations1）-3）.
Rarely do they occur due to the contiguous seeding of

Mycotic intracranial aneurysms (MIAs) are a focal

microbes onto the vascular wall, as observed in cases

weakening and dilatation of the arterial vessel wallsof meningitis or other parameningeal infection4）5）. The

mediated by microbial infections or toxin injury. They

anterior cerebral circulation is commonly implicatedcommonly follow septic embolization of bacterial orwith the middle cerebral artery (MCA), accounting for＊

Corresponding author : Toshihiro Ogiwara
Department of Neurosurgery, Shinshu University School of
Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
E-mail : togiwara@shinshu-u.ac.jp

No. 6, 2023

more than two-thirds in some series3）-6）. MIAs involv­
ing the vertebral-basilar system are uncommon andrarely reported to involve the posterior inferior cere­bellar artery (PICA)4）7）. To the best of our knowl­
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Campbell・Ogiwara・Abe et al.

Fig. 1 Cranial contrast-enhanced MRI showing enlargement of the left optic nerve sheath with contrast
enhancement, compared to the right (A). Repeat contrast cranial MRI 3 months later showed anenlarged optic nerve sheath with cavernous sinus involvement (B).

edge, this is the first reported distal PICA aneurysm

sults were essentially normal, and echocardiography

arising from meningitis following endoscopic endona­

did not reveal any cardiac vegetation. Cranial mag­sal transsphenoidal surgery.

netic resonance imaging (MRI) revealed enlargement

More than 70 ％ of patients present with catas­of the left optic nerve sheath extending into the optic

trophic intracranial hemorrhage due to the friablecanal, with associated perioptic contrast enhance­

nature of MIAs, which are therefore associated withment (Fig. 1A). The initial diagnosis was optic peri­

1）
3）
5）

high morbidity and mortality. Management isneuritis. Other differentials excluded were anti-

multidisciplinary, and options include clipping throughneutrophil cytoplasmic antibodies (ANCA)-associatedcraniotomy, endovascular coiling or trapping, andorbital vasculitis (excluded by negative p-ANCA andbypass surgery. For the optimal surgical decision, ac-ANCA), sarcoidosis (no hilar adenopathy and nor­variety of factors need to be considered, including

mal serum and cerebrospinal fluid (CSF) acetylcho­

the aneurysm location and peculiarities, comorbidi­linesterase) and IgG4-related ophthalmic diseaseties (especially cardiac disease) and the available(normal serum IgG4 concentrations). The neurology

1）
5）
6）
8）
9）

. Here we present a caseteam placed the patient empirically on high-dose ste­report of a rare MIA involving the distal PICA fol­roids (prednisolone 50 mg/day), after which he showed

lowing meningitis after endoscopic endonasal optic

an initial improvement in vision.

facilities and expertise

nerve decompression for optic nerve sheath tumors
and a review of the related literature.
Ⅱ

Case Presentation

A repeated cranial MRI was requested 1 month laterbecause the patient’s visual symptoms worsened, andhe experienced progressive orbital and left hemifacial
pain despite the high-dose steroid treatment ; we also

A 75-year-old man presented with a 2-year history

observed further swelling of the optic nerve sheathof progressively worsening visual impairment of thewith cavernous sinus involvement. Due to the non-left eye. He had previously experienced fungal sinusitis,

improvement with steroids, a decision was made towhich had been managed with endoscopic rhinosinus

obtain a biopsy via the left supraorbital keyhole ap­

surgery. He also reported to have gradually noticed

proach, and histology revealed an optic nerve sheathdouble vision and left facial pain.

meningioma with infiltrating cavernous sinus (Fig. 2).

Clinical examination showed a corrected visual acui­

Endoscopic endonasal optic nerve decompression

ty of 1.2 in both eyes, and a progressive worsening

with left optic nerve canal release was performed 1

on the left side at the follow-up. We also observed

month later because the patient’s left-eye vision had

left cranial nerve IV and VI palsies with associatedfurther worsened (to 0.05), and he subsequently un­

hypoesthesia involving the V1 and V2 divisions ofderwent intensity-modulated radiotherapy. The pa­

the trigeminal nerve. Cardiovascular examination re­tient noted some improvement after surgical release416

Shinshu Med J

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MIC following meningitis

Fig. 2 Histopathological findings reveal the tumor cells
have a fascicular arrangement with whorl formationand psammoma bodies, which were diagnosed asmeningotherial meningioma. (H & E staining, ×40)

Fig. 3 CT showing subarachnoid hemorrhage involving the basal and the suprachiasmatic cisterns with associatedintraventricular hemorrhage (A, B) and hydrocephalus with associated intraventricular haemorrhage (C).

and intensity-modulated radiotherapy ; however, 5pected. There were no features suggestive of CSF

days later, he experienced a rebound of facial painleakage. Therefore, he was hospitalized and antibiotics

and rapidly deteriorating vision then involving both

(CEZ) were initiated, which led to relief from fevereyes. Orbital inflammation after radiation was consid­

and improvement in laboratory data. Five days later

ered, and high-dose steroids were recommended.

admission (7 weeks after surgery), the patient col­This intervention resulted in some relief of orbital

lapsed with loss of consciousness and respiratory

and hemifacial pain and some visual improvements.

distress. The immediate Glasgow Coma Scale score

About 1 month after surgery, the patient’s vision

was E1V1M1, necessitating emergency intubation andhad further worsened and he had completely losttransfer to the intensive care unit for ventilatory sup­vision in his left eye, while also experiencing debili­

port. An emergency computed tomography scantating orbital and hemifacial pain. Another repeat

showed features of an extensive subarachnoid hem­cranial MRI scan showed features suggestive of anorrhage (SAH) with an epicenter at the posterior

optic sheath and canal infection extending to the cav­fossa, associated with intraventricular hemorrhage

ernous sinus (Fig. 1B). He became unwell with recur­

and acute hydrocephalus (Fig. 3).

rent episodes of fever that were uncontrollable with

Emergency computed tomography angiography

antipyretics. Leukocytosis and differential neutrophilia(CTA) revealed a left distal PICA aneurysm with as­

were also observed. Periorbital infection following en­sociated vasospasm. This contrasted with a similar

doscopic endonasal transsphenoidal surgery was sus­

CTA conducted 1 month earlier, which had been nor­No. 6, 2023

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Campbell・Ogiwara・Abe et al.

Fig. 4 A showing axial cut of CTA depicting the PICA without an associated aneurysm. B showing similar
cut conducted 1 month later, revealing a left PICA aneurysm. The arrow indicates the aneurysm.

Fig. 5 CTA reconstruction showing both PICAs without associated aneurysms (A). CTA reconstruction
conducted 1 month after the previous CTA showing a left PICA de-novo aneurysm with associatedvasospasm (B). Catheter angiography via the transradial route showing a left PICA aneurysm (C)and complete coil embolization (D).

mal (Fig. 4, 5). Based on this clinical course and find­patient remained ventilator-dependent and showed

ings of neuroimages, a diagnosis of a ruptured left

no significant neurological recovery. Later, antibiotics

PICA mycotic aneurysm with acute hydrocephalus

were switched to sensitivity determined (MEPM)(SAH World Federation of Neurological Surgeons

when CSF sampling revealed an increasing CSF cell

(WFNS) grade 5) was made, and the patient’s rela­count (55/μl) and decreasing CSF glucose (23 mg/dl),

tives were informed of the diagnosis and prognosis.

indicative of Pseudomonas aeruginosa infection. He

The patient underwent emergency endovascular coilpassed away due to cardiac arrest 14 days after theembolization of the left PICA aneurysm on the same

initial incident.

day and external ventricular drainage to manage thehydrocephalus. Endovascular therapy was successful,and the aneurysm was well secured. However, the418

ⅢDiscussion

MIAs account for 0.7-6.5 ％ of cerebral aneurysms,
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MIC following meningitis

although more than twice the incidence has been re­
1）
5）
8）

complicated by endonasal transsphenoidal surgery.

. The term “mycotic” was

MIAs are distally located, often dysmorphic, friable,

first described by William Osler in his Gulstonianand have a wide or non-demonstrable neck. The fu­

lectures, referring to the mushroom appearance of thesiform morphology is the most common, accounting

aneurysm resembling budding fungus on the aorta8）10）.

for 52.5 ％, while the saccular type is seen in 45 ％Although the more accurate term should be “infected

and may occur in multiples in up to 25 ％ of cases1）5）6）.

aneurysm”, the older term has persisted in the litera­

The infectious cascade is triggered by embolization

ture. Here we present a case of a ruptured PICA my­of the organism lodging in the distal intracranial ves­

cotic aneurysm secondary to meningitis complicating

sels, causing septic infarction, or in the vaso-vasorum,transsphenoidal intervention, highlighting the ex­triggering an inflammatory cascade. Neutrophil infil­

tremely rare possibility of contiguous infection caus­

tration occurs within the media and adventitia, re­ing an aneurysm in the posterior circulation.

sulting in the release of cytokines and proinflamma­Ａ

tory factors, including various proteases and matrix

ported in autopsy series

Etiology and risk factors
Large population studies on MIAs are lacking due

metalloproteins 1, 8, & 91）6）9）14）. Degradation of theto their rarity ; however, an extensive systematic

arterial wall occurs with accompanying intimal prolif­

review of case reports and series by Alawieh et al.

eration and fragmentation of the internal elastic lami­

showed that infective endocarditis was the primaryna. The combination of vessel wall destruction andcause in almost 70 ％ of MIA cases, especially withshear stress from the hydrostatic pressure of the blood

5）

vegetations in the left cardiac chamber . The au­

flow results in focal dilatation of the vessels1）9）14）.

thors also implicated dental infection as an important

Bacterial infections are the most common cause of

etiologic factor accounting for 10.7 ％ of cases. Other

MIAs, seen in 80 ％ of cases, and predominantly in­less common factors include meningitis, orbital cellu­

volve gram-positive cocci1）5）6）. In addition, almost one-

litis, mastoid infections, and cavernous sinus throm­

third of cases are caused by gram-negative organ­

bosis5）6）11）. Immunosuppression from chronic steroid

isms, as seen in this index case, and usually follow

use and other immunosuppressants, especially seen incontiguous infections14）. One systematic review hasorgan recipients or patients with acquired immuno­

implicated fungal infections in 13.4 ％ of cases, with

deficiency syndrome, is a known risk factor and is

Aspergillus species being the most common and as­

frequently associated with fastidious organisms in­sociated with immunosuppression5）. In rare cases,cluding fungi and protozoa5）6）11）-13）. Invasive cranial

varicella zoster virus and HIV 1 and 2 are the caus­intervention such as endoscopic endonasal trans­

ative organisms1）6）.

sphenoidal surgery, prolonged steroid use, and radia­Ｃtion therapy were risk factors of meningitis in thisClinical presentation and diagnosis
Most MIAs are noticed after rupture, resulting inindex case that predisposed the patient to MIA.

subarachnoid and intraparenchymal hemorrhage

Ｂ

Pathoanatomy and microbiology of MIAs

(IPH)8）11）15）. IPH is more common in MIAs than in

The MCA is the most frequently implicated vessel,

other berry aneurysms because of their friable naturein 50-78 ％ of reported MIA cases, and are related toand distal location within the brain parenchyma.

the higher differential flow from the internal carotid

Ruptured MIAs are usually catastrophic and present

1）
3）
5）
-7）

artery. Most posterior circulation MIAs involvewith a high WFNS grade, with mortality approaching

the posterior cerebral arteries, which are terminal

80 ％ in some series1）3）15）16）. Other authors have opinedbranches of the basilar artery, but rarely the proxi­

that minor focal deficits from distant embolization of

mal tributaries

1）5）. Piccirilli et al.

4）reported the firstcase of an infective PICA aneurysm following dental

septic foci are more frequent and usually go unno­
ticed6）.

infection treated approximately 2 years prior ; however,The diagnosis of MIA involves the demonstration

none have been reported following bacterial meningitisof an intracranial aneurysm using an appropriate im­

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Campbell・Ogiwara・Abe et al.
Table 1

Validated criteria for diagnosis of mycotic intracranial aneurysm17）

Mandatory criteria

Intracranial aneurysm on neurovascular imaging

Supportive criteria

Presence of recent or predisposing infection : (1) infective endocarditis, (2) meningitis,(3) orbital cellulitis, (4) cavernous sinus thrombophlebitis
Angiographic features : (5) multiplicity, (6) distal location, (7) fusiform shape, (8) change
is the shape and size of a new aneurysm on follow-up imaging.
Other contributory factors : (9) age ＜45 years, (10) fever/history of fever ≥ 7 days, (11)recent lumbar puncture, (12) intraparenchymal haemorrhage in brain imaging.

Definitive MIA : presence of mandatory criteria and any three or more supportive criteria. Clinical probable
MIA : mandatory criteria and two of the supportive criteria. Clinically probable MIA : mandatory criteria and oneof the supportive criteria. Our patient had the mandatory criteria and four supportive criteria9）17）.

aging modality along with the presence of predispos­

there has been rapid advancement in endovascular

ing factors, as described earlier. A scoring systemtechniques (EVTs) for aneurysms, reflected in thedevised by Kannoth et al. suggested that an intracra­

increased number of MIAs treated with these tech­nial aneurysm on neuroimaging with three or moreniques1）5）8）18）. EVTs offer numerous advantages, es­associated supportive criteria indicates a definitive

pecially in high-risk patients with a high WFNS

17）

diagnosis of MIA (Table 1) . The angiographic fea­

grade and significant anesthesia risk, can reach sur­tures of MIAs include their fusiform shape, distal

gically inaccessible areas, and offer a cure for multi­

location, multiplicity, dysmorphic nature, and change

ple aneurysms in one sitting. They also allow for

1）
6）. Whileearly cardiac surgery in patients with valvular dys­

digital subtraction angiography remains the gold

function, as anticoagulation therapy can be com­standard for diagnosing MIAs, CTA and magnetic

menced as early as 24 hr after EVT1）6）. Various EVT

resonance angiography (MRA) are more commonly

options, including coil embolization, stent-assisted

utilized due to their less invasive nature and easy

coiling, flow diverters, and liquid embolization agents,

availability of these modalities. However, in acuteare available1）2）5）6）8）19）. The index case presented here

emergencies, a non-contrast computed tomography

underwent successful aneurysm coil embolization onscan can demonstrate features of SAH, IPH, associat­

the rupture day ; however, the patient succumbed to

ed brain edema, hydrocephalus, and herniation syn­his illness due to irreversible herniation syndrome

drome, thereby guiding management. Identifying theand infection.

in shape or size on follow-up angiography

causative organisms in the blood or CSF is pivotal in

Microsurgical clipping is the option of choice for rup­

deciding the proper definitive antibiotic course, andtured MIAs with associated IPH, unfavorable aneu­

blood cultures may be positive in 35-75 ％ of patientsrysm morphology, or failed EVT interventions1）5）6）8）15）.

with infective endocarditis1）6）14）. Serial inflammatory

Additionally, microsurgical clipping is employed tomarker assessment should be used to determine

raise intracranial pressure with associated herniation

responses to antibiotic therapy and follow-up.

syndrome requiring decompression or CSF diversion.

Ｄ

Microvascular clipping is more challenging in MIAs

Management options for MIAs
There is lack of level-one evidence to create guide­than in conventional aneurysms because of the friablelines for the treatment of MIAs because of theirwall and distal location of the former and the mor­rarity ; nevertheless, management options are guided

phological complexity of the neck. Ohtake et al. ana­

by the aneurysmal characteristics, rupture status,

lyzed 129 MIAs and noted that almost two-thirds ofpresence of comorbidities, including concomitant car­patients presented with ruptures and no relationshipdiac disease, and need for cardiac surgery and avail­

between rupture status and the location or size ofability of care facilities1）2）5）6）8）9）. Over the last decade,their aneurysm8）. In addition, 63 patients in their se­

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MIC following meningitis

ries underwent surgical interventions (55.6 ％ under­

geons, neurointerventionists, intensivists, and otherwent EVT procedures and 44.4 ％ had open sur­care physicians, including cardiac surgeons. Decisiongery) ; however, no significant difference was notedmaking must involve the family and caregiver, andin the outcome between both groups (p＝0.867). In

consideration of the patient’s physical status, comor­

contrast, a larger systematic review by Alawieh etbidities, and aneurysm characteristics is essential.

5）

al . involving more patients showed the superiority

The prognosis for ruptured MIAs is poor, especiallyof EVTs over open surgery in terms of mortality andin moribund patients with cardiac disease.

overall outcomes.

Ⅳ Conclusions

Conservative therapy is reserved for unruptured
aneurysms with a high surgical risk, defined by mor­

MIAs arising from the PICA following meningitis

phological characteristics, rendering them non-are rare, but complications following surgical inter­

1）6）

.

vention and rupture are associated with high mor­

In such a scenario, antibiotic therapy based on cul­

bidity and mortality. Maintaining a high index ofture results is commenced, followed by serial angio­

suspicion and pursuing early intervention before

graphic monitoring. Response to therapy is describedrupture could potentially prevent adverse outcomes.

as a reduction in the size or disappearance of thePatient care should be approached in a multimodal,

aneurysm. Therapy failure occurs when the MIA

multidisciplinary, and individualized manner. Nota­

ruptures, increases in size, or remains the same de­bly, endovascular therapy stands as the treatment

spite antibiotic use or the occurrence of new aneu­

modality of choice, proving effective, particularly inamenable to EVT and microvascular approaches

1）
6）

rysms

. Invasive therapy with microsurgical clip­

high-risk cases of ruptured MIAs.

ping or EVT procedures are then warranted. Matsubara

Compliance with Ethical Standards

and colleagues suggested a multimodal approach toConflict of interest

the treatment of MIAs and possibly conservative
treatment with antibiotics and serial imaging in un­
20）

ruptured and clinically stable patients . They noted

The authors declare that they have no conflict ofinterest.

disappearance without recurrence or rebleeding of

Ethical Approval

seven unruptured MIAs managed following that
protocol ; however, Ohtake et al. found that although

All procedures described in this report were per­antibiotic treatment is more effective in unruptured

formed in accordance with the ethical standards ofcases, it is associated with high mortality and mostthe institutional and/or national research committee

8）patients require additional surgery .

and the 1964 Helsinki Declaration and its later amend­

Care for MIAs should be multidisciplinary andmultimodal, with close collaboration among neurosur­

ments or comparable ethical standards. Informed
consent was obtained from the patient.

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