CT cerebral venography (protocol)

CT cerebral venography (also known as a CTV head or CT venogram) is a contrast-enhanced examination with an acquisition delay providing an accurate detailed depiction of the cerebral venous system. 

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' preference, institutional protocols, patient factors (e.g. allergy) and time constraints. 

Indications

A CT venogram is obtained in a number of clinical scenarios where anatomy and patency of the cerebral veins is required. It is an alternative to MR venography. Indications include the diagnosis of cerebral venous thrombosis and preoperative anatomy particularly for posterior fossa surgery where the sigmoid sinuses may be compressed (e.g. retrosigmoid craniotomies). 

Purpose

The purpose of this exam is to visualize the cerebral veins and venous sinuses filled with contrast opacified blood, allowing their anatomy and patency to be assessed. 

Contraindications

IV iodinated contrast contraindications, such as chronic renal failure and allergy. 

Technique

• patient position
  • supine with their arms by their side
• scout
  • CT to the vertex
• scan extent
  • CT to the vertex
• scan direction
  • caudocranial
• contrast injection considerations
  • injection 
    • 75-100 ml of non-ionic iodinated contrast
• scan delay
  • 45 seconds (see practical points)
• ​respiration phase
  • ​suspended 

Data acquisition and analysis

• images are analyzed on a dedicated workstation
• proper evaluation of the dural sinuses indicates proper inspection of the axial thin-section contrast-enhanced source images of a helical CT scan
• two-dimensional (2D) & three-dimensional (3D) multiplanar images, as well as rendering techniques such as maximum intensity projection (MIP), surface shaded displays (SSD) and volume rendering (VR) in a sagittal, coronal, and oblique planes
• an essential step in CT venography is the removal of bone from the images, by graded subtraction

Findings

Venous sinus abnormalities

• dural venous sinus thrombosis
• thrombosis recanalization, the sinus shows an irregular appearance with multiple intrasinus channels and dural collateral vessels
• sinus stenosis or occlusion secondary to tumor invasion (e.g. meningioma)
• vascular malformations (e.g. AVM, dural arteriovenous fistula or developmental venous anomaly)
• idiopathic intracranial hypertension: bilateral stenoses of the transverse sinuses, without definitive evidence of current or prior thrombosis

Parenchymal abnormalities

• cerebral parenchymal abnormalities such as hemorrhagic infarction

Variant anatomy

• sinus hypoplasia and aplasia
• arachnoid granulations
• sinus duplication or fenestration
• variant anatomy of the sinuses (e.g. occipital sinus or persistent falcine sinus)

Practical points

Caution must be taken to achieve a well-timed acquisition in CT cerebral venography, particularly in cases of intracranial hypertension which can cause delayed filling of the venous sinus. A premature acquisition may create a false impression of thrombosis, which is simply due to contrast not yet reaching the venous sinuses - if the cerebral veins are not opacified on a CT cerebral venogram, premature acquisition should be suspected.