Infectious intracranial aneurysm

Infectious intracranial aneurysm (IIA), also known as mycotic aneurysm, is a rare form of aneurysm that occurs within the cranium (skull) due to an infection. These aneurysms are typically associated with bacterial or fungal infections that affect the arterial walls, leading to their weakening and subsequent ballooning. The term "mycotic" historically referred to fungal infections, but in the context of IIA, it encompasses any infection of the arterial wall, not limited to fungal etiologies.

Causes

Infectious intracranial aneurysms are most commonly caused by bacterial infections, with the Staphylococcus aureus and Streptococcus species being the predominant pathogens. These infections can reach the cerebral arteries through various routes, including septic emboli from a distant infectious source (e.g., endocarditis), direct extension from adjacent infections (such as sinusitis or mastoiditis), or as a complication of bacterial meningitis. Fungal causes, though less common, include species such as Aspergillus and Candida.

Pathophysiology

The pathogenesis of IIA involves the infection of the arterial wall, leading to its weakening. Infectious agents can invade the arterial wall directly or via circulating emboli. Once the arterial wall is infected, it can lead to the formation of an aneurysm through inflammatory damage and necrosis of the vessel wall. This process weakens the structural integrity of the artery, causing it to dilate and form an aneurysm.

Symptoms

Symptoms of an infectious intracranial aneurysm can vary widely depending on the aneurysm's size, location, and rate of growth. Common symptoms include headache, nausea, vomiting, neurological deficits (such as weakness or numbness in parts of the body), and in severe cases, subarachnoid hemorrhage (SAH) due to rupture of the aneurysm. SAH presents with a sudden, severe headache often described as the "worst headache of one's life," along with neck stiffness, photophobia, and possibly loss of consciousness.

Diagnosis

Diagnosis of IIA involves a combination of clinical assessment, laboratory tests, and imaging studies. Blood cultures may identify the causative organism. Imaging techniques such as computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are crucial for visualizing the aneurysm's size, location, and relation to surrounding structures. In some cases, digital subtraction angiography (DSA) may be employed for a more detailed view.

Treatment

Treatment of infectious intracranial aneurysms is complex and typically involves a combination of antimicrobial therapy and surgical or endovascular interventions. The choice of treatment depends on several factors, including the aneurysm's size, location, and the patient's overall health status. Antimicrobial therapy is tailored based on the identified organism and its antibiotic sensitivities. Surgical options may include aneurysm clipping or excision, while endovascular techniques can involve coil embolization or stenting.

Prognosis

The prognosis for patients with IIA varies and depends on the aneurysm's size, location, the causative organism, and the timeliness and effectiveness of treatment. Early diagnosis and appropriate treatment are crucial for improving outcomes. Without treatment, the risk of aneurysm rupture and subsequent SAH is high, which significantly increases morbidity and mortality rates.