Based on that CT report + the clinical history (sunsetting eyes, lethargy, raised BP, ?raised ICP), the top 3 differentials for the cause of this pattern of haemorrhage are:
1) Ruptured intracranial aneurysm (subarachnoid haemorrhage)
Why it fits:
The haemorrhage is centred in the quadrigeminal cistern / perimesencephalic cistern, which is a classic subarachnoid location.
There is intraventricular extension (blood in lateral + 3rd ventricles), which can happen with aneurysmal SAH.
Obstructive hydrocephalus is very common after SAH/IVH.
No trauma features → makes spontaneous SAH more likely.
Most likely aneurysm territories in this region:
Posterior circulation aneurysms (e.g. basilar tip, PCA, SCA).
2) Vascular malformation (AVM / AV fistula / cavernoma)
Why it fits:
AVMs or fistulas can cause large-volume haemorrhage, including subarachnoid + intraventricular blood.
Posterior fossa / deep midline vascular lesions can bleed into cisterns and ventricles.
This is especially important in neonates/infants where vascular causes are a key concern.
Clue in the report:
They explicitly recommend MRI/US “for evaluation of underlying vascular or structural abnormality” — that’s radiology code for “we’re worried this could be vascular.”
3) Neonatal/intraventricular haemorrhage related to prematurity or germinal matrix bleed (with secondary hydrocephalus)
Why it fits:
The report strongly suggests this is a neonate (“neonatal intensive care input”, cranial ultrasound).
Neonatal IVH can cause acute obstructive hydrocephalus, lethargy, sunsetting eyes, and raised BP (Cushing response).
Although classic germinal matrix IVH is more anterior (caudothalamic groove), severe IVH can track widely through the ventricles and cause secondary cisternal blood.
Why it’s slightly less perfect than #1–2:
The centre of haemorrhage being described as quadrigeminal/perimesencephalic cistern is more “subarachnoid-first” than “ventricular-first.”
Practical next-step thought (what the team will usually do)
Urgent neurosurgical review (likely CSF diversion: EVD/VP shunt depending on stability).
Cranial ultrasound (fast bedside).
MRI brain ± MRA/MRV when stable.
Often CTA/MRA is considered specifically to look for posterior circulation aneurysm/AVM.
If you want, I can also give you a one-liner impression (exam-style) or help you phrase the top ddx in a radiology report style.
