Basilar and posterior cerebral artery hyperdense clots

Case contributed by Mohammad Al-Tibi


Six days post C-section, presents with agitation , low GCS, blurred vision and fixed dilated left pupil.

Patient Data

Age: 30 years
Gender: Female

29 weeks pregnant female with COVID-19 pneumonia had emergency lower segment C-section under GA due to severe respiratory distress. Following extubation, she became agitated, hypoxic, and developed new blurry vision and fixed dilated left pupil.

Uncontrasted CT head (with stroke window)


There is wedge-shaped hypodensity involving the PCA territories bilaterally, worse on the left with loss of grey-white matter differentiation in keeping with ischemic infarct. The infarct also involves the left cerebral peduncle/ midbrain and both cerebellar hemispheres.

Allowing for the extensive streak artefacts in the posterior fossa, there is a well-defined hyperdensity in the basilar artery concerning for a hyperdense basilar artery thrombus. Another hyperdense clot is noted along the P1 segment of the left PCA.

Otherwise, no intracranial bleeding or extradural collection. No significant edema or mass effect. No midline shift or hydrocephalus.

A decision was made to perform an intracranial angiogram.

CT intracranial angiogram


There is a filling defect in the top of basilar artery at the level of the midbrain. Similarly, there is filling defect in P1 segment of the left PCA. These correlate with the hyperdense clots seen in the non-contrasted phase.

Normal contrast is opacification in the remainder of the branches of circle of Willis with no evidence of contrast extravasation or large aneurysmal dilatation.

Annotated images of hyperdense clot signs with corresponding filling defects


These annotated images are windowed to reduce the beam hardening artefact from patient's earrings. The first two images demonstrate hyperdense clot in P1 segment of the left PCA with corresponding filling defect on angiogram phase. The second two images outline the hyperdense clot in the base of the basilar artery with a corresponding filling defect in the arterial phase.

Case Discussion

Three key messages:

  • It is not uncommon to miss a basilar artery hyperdense clot, especially in the presence of extensive metallic artifacts as shown above. It is crucial to have a high index of suspicion for top of the basilar syndrome when a there is a typical history of visual disturbance, fixed pupils, reduced GCS and agitation.
  • One should be mindful of the common ''satisfaction of search'' trap. It's infrequent to have two hyperdense clots on one scan.
  • Lastly, if in doubt, performing intracranial angiogram would either confirm or refute suspicion.

This lady - unfortunately- passed away as was not deemed suitable for thrombectomy.

How to use cases

You can use Radiopaedia cases in a variety of ways to help you learn and teach.

Creating your own cases is easy.

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.