An infectious intracranial aneurysm (IIA, also called mycotic aneurysm) is a

cerebral aneurysm An intracranial aneurysm, also known as a brain aneurysm, is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel. Aneurysms in the posterior circul ...

that is caused by

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

of the cerebral

arterial wall An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...

Signs and symptoms

Many patients with unruptured IIA may have no symptoms. In patients who do have symptoms these are often related to rupture of the aneurysm and to its cause. Rupture of an IIA results in

subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of consci ...

, symptoms of which include headache, dizziness, seizures, altered mental status and focal

neurological deficit Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal c ...

s. In contrast to other cerebral aneurysms, large aneurysm size does not increase the chance of rupture. Small IIAs tend to have high rupture rates, while larger IIAs more commonly cause symptoms due to pressure on the surrounding brain tissue.

Cause

Most IIAs are caused by bacterial infection, most commonly ''

Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive ...

'' and ''

Streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs ...

'' species. In most cases the infection originates from left-sided

bacterial endocarditis Infective endocarditis is an infection of the inner surface of the heart, usually the valves. Signs and symptoms may include fever, small areas of bleeding into the skin, heart murmur, feeling tired, and low red blood cell count. Complications ...

. Other common sources include

cavernous sinus thrombosis The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The cave ...

bacterial meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

, poor

dental hygiene Oral hygiene is the practice of keeping one's mouth clean and free of disease and other problems (e.g. bad breath) by regular brushing of the teeth (dental hygiene) and cleaning between the teeth. It is important that oral hygiene be carried out ...

and

intravenous drug Drug injection is a method of introducing a drug into the bloodstream via a hollow hypodermic needle, which is pierced through the skin into the body (usually intravenously, but also at an intramuscular or Subcutaneous injection, subcutaneous l ...

use. The use of the term infectious aneurysm by the above authors is incorrect. Refer to Holtzman RNN, Pile-Spellman JMD, Brust JCM, Hughes JEO, Dickinson PCT: Surgical Management of Intracranial Aneurysms Caussed by Infection, in: Schmidek HH and Roberts DW(eds): Schmidek & Sweet Operative Neurosurgical Techniques: Indications, Methods, and Results ed.5. Philadelphia: Elsevier Inc. 2006 Vol 1: Chap. 87, pp1223-1259

Diagnosis

Diagnosis of IIA is based on finding an intracranial aneurysm on vascular imaging in the presence of predisposing infectious conditions. Positive

bacterial culture A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagn ...

s from blood or the infected aneurysm wall itself may confirm the diagnosis, however blood cultures are often negative. Other supporting findings include

leukocytosis Leukocytosis is a condition in which the white cell (leukocyte count) is above the normal range in the blood. It is frequently a sign of an inflammatory response, most commonly the result of infection, but may also occur following certain parasit ...

, an elevated

erythrocyte sedimentation rate The erythrocyte sedimentation rate (ESR or sed rate) is the rate at which red blood cells in anticoagulated whole blood descend in a standardized tube over a period of one hour. It is a common hematology test, and is a non-specific measure of ...

and elevated

C-reactive protein C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin-6 ...

in blood.

Terminology

The term ''mycotic aneurysm'', initially attributed to Osler and used to describe bacterial intracranial aneurysms, is a misnomer. Most investigators currently agree that its use should be strictly limited to descriptions of aneurysms of fungal origin. Yet efforts to establish an accurate nomenclature have been generally unsuccessful. Therefore, we are resigned to the fact that the term mycotic aneurysm will remain in general parlance. At the same time, we prefer the use of a more specific and accurate heading, namely, ''infected intracranial aneurysm'', to include the categories of intracranial bacterial aneurysm, fungal aneurysm, spirochetal aneurysm, infested or amebic aneurysm, viral aneurysm and phytotic aneurysm, according to the specific infecting organism or agent. The terms ''infectious aneurysm'' and ''infective aneurysm'' are flawed because they imply that the aneurysm itself is the infecting agent rather than being the end point of an infecting process. Until such a pathogenesis has been detected, it is the intention of the authors to avoid catachresis and the application of archaic language (Marcus S, The George Delacorte Professor of English and Comparative Literature, Columbia University, New York, personal communication, 1993: "The correct usage is 'infected'. The term 'infectious' died out as a usage in termed of infected in 1726." And Jost, DA, former senior lexicographer of ''The American Heritage Dictionary'', Boston, personal communication, 1996: "''Infectious aneurysm'' will be interpreted by most users of English as an aneurysm that can communicate infection"). The term ''infected intracranial aneurysm'' lacks the properties of complete definition because it refers to the initial process that affects the arterial wall and to aneurysms found to have bacteria in their walls at the time of excision (Table 87-1, Patient 3; see Case Report 9, Fig. 87-9), but not to the processes of focal dilatation or subsequent aneurysm formation and enlargement. It also accurately describes the congenital or berry aneurysm that has become secondarily infected. The terms ''septic aneurysm'' and ''septic embolism'' and ''septic arteritis'' are also commonly used. However, the word septic refers to infection involving the blood stream and is not really descriptive of the aneurysm themselves.

Treatment

Treatment depends on whether the aneurysm is ruptured and may involve a combination of

antimicrobial drug An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...

and/or endovascular treatment.

Prognosis

Mortality Mortality is the state of being mortal, or susceptible to death; the opposite of immortality. Mortality may also refer to: * Fish mortality, a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock throug ...

of IIA is high, unruptured IIA are associated with a mortality reaching 30%, while ruptured IIA has a mortality of up to 80%. IIAs caused by

fungal infections Fungal infection, also known as mycosis, is disease caused by fungi. Different types are traditionally divided according to the part of the body affected; superficial, subcutaneous, and systemic. Superficial fungal infections include common ti ...

have a worse prognosis than those caused by bacterial infection.

Epidemiology

IIAs are uncommon, accounting for 2.6% to 6% of all

intracranial aneurysm An intracranial aneurysm, also known as a brain aneurysm, is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel. Aneurysms in the posterior circul ...

s in autopsy studies.

References

{{Vascular diseases Neurosurgery Cerebrovascular diseases