Hemorrhage patterns: where to look for the ruptured aneurysm?
The distribution pattern of blood on non-contrast CT allows predicting the localization of the damaged vessel with a high degree of probability. In severe cases, diffuse massive filling of the basal cisterns is observed, but local hematomas provide clear diagnostic clues:
- Anterior communicating artery (ACoA): blood accumulates in the septum pellucidum (septum pellucidum), can spread into the frontal lobes and form a focal hematoma (often involving the inferior temporal lobe).
- Middle cerebral artery (MCA): the clot is localized asynchronously, predominantly in the Sylvian fissure on the side of the rupture.
- Basilar artery tip: blood fills the interpeduncular fossa, spreading to the brainstem and thalami. The prognosis for this variant is usually unfavorable.
- Posterior inferior cerebellar artery (PICA): the hematoma is visualized at the brainstem level, in the craniocervical junction area, and often ruptures into the ventricular system (via the fourth ventricle).
- Perimesencephalic SAH: a small blood collection is limited to the interpeduncular fossa. This is a specific, prognostically favorable non-aneurysmal variant (likely of venous origin) where structural arterial anomalies are not detected.
Subacute and chronic period complications
In the first days and weeks following hemorrhage, CT and MRI visualize secondary changes that largely determine the outcome of the disease:
- Acute communicating hydrocephalus. Blood clots disrupt CSF outflow, leading to ventricular dilation (temporal horns expand first). Often resolves spontaneously, but may require CSF diversion.
- Ischemia due to vasospasm. Occurs between 4 and 11 days after rupture. The risk is higher when the volume of escaped subarachnoid blood is greater.
- Chronic recurrent SAH. Clinically manifests as cognitive decline, ataxia, and lower cranial nerve palsies. MRI (T2* GRE or SWI sequences) reveals signs of superficial siderosis—deposition of hemosiderin in the leptomeninges (leptomeninges), especially around the midbrain.
Instrumental diagnostics algorithm
Acute SAH requires immediate evaluation of intracranial vessels:
- CT angiography (CTA): the standard for initial assessment. The method is fast (<10 seconds), non-invasive, and sensitive. It is important to carefully examine source slices and 3D reconstructions, especially at the skull base where bone can obscure small defects.
- Digital subtraction angiography (DSA): the gold standard. If CTA is negative in the presence of SAH clinical presentation, performing DSA to search for small vascular malformations is routine practice.
- Magnetic resonance angiography (MRA): the method of choice in the non-acute period (e.g., 3D TOF technique). Used for family screening and post-treatment follow-up. On spin-echo, a patent aneurysm appears as a signal void area — the flow void phenomenon.
Management tactics
To exclude the ruptured aneurysm from the bloodstream, endovascular coil embolization (coiling) or open microsurgical clipping is used. The endovascular approach shows better outcomes one year post-procedure, but is accompanied by a slightly higher risk of future re-bleeding.
Management of unruptured aneurysms: According to the ISUIA study, incidental anterior circulation aneurysms measuring ≤ 7 mm do not require surgical treatment if the patient has no history of SAH, as elective surgery risks outweigh the risk of spontaneous rupture. Preference is given to surgery for large lesions and posterior circulation aneurysms.
Briefly: answers to topical questions
Why does vasospasm occur with a delayed onset after subarachnoid hemorrhage?
Vasospasm following subarachnoid hemorrhage occurs with a delayed onset due to the effects of vasoactive substances present in the escaped blood. This complication typically develops between 4 and 11 days after the initial episode. The probability of its occurrence is higher when a large volume of subarachnoid blood is present on the initial computed tomography scan. The most formidable consequence of this condition is the development of cerebral infarction, and vasospasm itself severely complicates accurate diagnosis and effective treatment.
What scales are used for radiological assessment of subarachnoid hemorrhage severity on CT?
The Fisher scale and its modified version are used for radiological assessment of subarachnoid hemorrhage severity on computed tomography.
- Original Fisher scale (Fisher scale) — evaluates the presence and thickness of the blood layer, as well as the presence of intracerebral hematoma or intraventricular hemorrhage.
- Modified Fisher scale (modified Fisher scale) — also accounts for the thickness of the subarachnoid blood layer (thin or thick layer > 1 mm) and the presence of concomitant intraventricular hemorrhage.
What are the advantages and disadvantages of endovascular aneurysm embolization compared to microsurgical clipping?
Endovascular embolization is a less invasive method compared to open microsurgical clipping, but carries a higher risk of recurrent hemorrhage.
| Characteristic | Endovascular embolization | Microsurgical clipping |
|---|---|---|
| Invasiveness | Less invasive procedure | High invasiveness (requires craniotomy) |
| Outcomes (1 year) | Better outcomes (lower mortality/disability rate) | Higher rate of mortality or disability |
| Epilepsy risk | Lower | Higher |
| Re-bleeding | Higher rate (re-bleeding) | Most effective prevention method |
| Complications | Risk of coil prolapse | Risk of serious postoperative complications |
The rule of thirds for aneurysms: ~33% — anterior communicating artery, ~33% — posterior communicating artery, 20% — middle cerebral artery. In total, the carotid circulation accounts for about 90% of all defects.
Class and exam questions
Why is vasospasm considered a delayed complication?
In most neurosurgical centers, confirming a negative CTA with digital subtraction angiography (DSA) is routine practice to avoid missing microaneurysms or other hidden malformations.
How does the patent lumen of an aneurysm appear on MRI?
In spin-echo mode, blood flowing through the aneurysm creates a signal void area—the so-called flow void phenomenon.
Is surgical intervention necessary for an incidental 5 mm anterior cerebral artery aneurysm?
If there is no history of subarachnoid hemorrhage, according to ISUIA criteria, anterior circulation aneurysms ≤ 7 mm in diameter do not require surgical treatment.
What else to study on this topic
- Morphological classification of cerebral aneurysms (saccular, fusiform, dissecting).
- Imaging features of mycotic and giant intracranial aneurysms.
- Clinical presentation of oculomotor nerve compression in posterior communicating artery aneurysm.
- Limitations of 3D TOF MRA in detecting small internal carotid artery siphon aneurysms.
- Causes of pseudo-pathological FLAIR signals in the basal cisterns (CSF pulsation artifacts).
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