How should I perform a CT head venography in an adult patient, including indications, contraindications, preparation, contrast protocol, scanning parameters, and image reconstruction?

CT Head Venography: Technical Protocol and Clinical Application

CT venography (CTV) of the head should be performed as a contrast-enhanced study following a non-contrast CT, using thin-section helical acquisition with venous-phase timing (typically 40-60 seconds post-injection), followed by maximum intensity projection (MIP) reconstructions for optimal visualization of the intracranial venous system. 1, 2

Primary Indications

CTV head is indicated when there is clinical or imaging suspicion of:

• Dural venous sinus thrombosis – the most common indication, particularly in patients with orthostatic headache, new-onset seizures, or unexplained intracranial hemorrhage 1, 2
• Venous complications of sinusitis – including venous thrombophlebitis in pediatric or adult patients 1
• Evaluation of vascular malformations – particularly when venous drainage patterns need assessment 1
• Post-traumatic venous injury – though not first-line in acute trauma settings 1
• Young patients (<70 years) with lobar intracerebral hemorrhage – to exclude cerebral venous thrombosis as an underlying cause 3

Contraindications

• Severe contrast allergy – consider MR venography as alternative 1
• Significant renal impairment – MRV without contrast may be preferred 4
• Pregnancy – MRV is preferred to avoid radiation exposure 1

Patient Preparation

• Verify renal function (creatinine/eGFR) before contrast administration 1
• Confirm absence of contrast allergy history 1
• Ensure adequate IV access (18-20 gauge preferred) for power injection 5
• No fasting required for routine CTV 5

Contrast Protocol

Contrast administration parameters:

• Iodinated contrast volume: 80-120 mL (typically 100 mL) 6, 5
• Injection rate: 3-4 mL/second via power injector 5
• Timing: Venous phase acquisition at 40-60 seconds post-injection (may extend to 70 seconds for optimal venous opacification) 6, 5
• Saline flush: 30-50 mL following contrast to optimize vessel opacification 5

Scanning Parameters

Technical acquisition specifications:

• Slice thickness: Thin-section helical CT with 0.5-1.25 mm collimation 5
• Coverage: Skull base to vertex, encompassing entire intracranial venous system 1, 6
• kVp: 120 kVp (standard adult protocol) 5
• Tube current: Adjusted for patient size (typically 200-300 mAs) 5
• Pitch: 0.5-1.0 for helical acquisition 5

The study should be performed immediately after non-contrast CT while the patient remains on the scanner table to avoid diagnostic delays. 3

Image Reconstruction

Post-processing techniques are essential for optimal interpretation:

• Maximum intensity projection (MIP) images – primary reconstruction method for venographic display in multiple planes (axial, coronal, sagittal) 7, 6, 5
• Matched mask bone elimination (MMBE) – automated bone removal technique that provides excellent visualization with 100% adequate bone removal in clinical studies 7
• Integral algorithm display – allows direct visualization of thrombus within sinuses by depicting average intensity values 6
• Axial source images – must be reviewed alongside reconstructions to avoid missing subtle findings 7
• 3D volume-rendered images – optional for surgical planning or complex anatomy 5

Anatomical Structures Evaluated

CTV consistently visualizes the following structures:

• Superior sagittal sinus – identified in 100% of studies 5
• Transverse sinuses (bilateral) – identified in 100% of studies 5
• Straight sinus – identified in 100% of studies 5
• Sigmoid sinuses (bilateral) 6
• Internal cerebral veins 6, 5
• Vein of Galen 5
• Cortical veins – superficial and deep systems 5

Diagnostic Performance

CTV demonstrates high accuracy for cerebral venous thrombosis:

• Sensitivity: 75-100% depending on the specific sinus/vein involved 6
• Specificity: 75-100% when compared to MR venography as reference standard 6
• Interobserver agreement: Excellent (kappa = 0.83 per patient; kappa = 0.76 per sinus/vein) 7
• Comparison to MRV: CTV is as accurate as MRV for diagnosing cerebral venous thrombosis, with fewer artifacts and easier interpretation 6, 5

Imaging Findings in Venous Thrombosis

Direct signs of thrombosis on CTV:

• Filling defect within the sinus lumen (non-occlusive thrombosis) 2
• Complete non-filling of the sinus (occlusive thrombosis) with "cupping appearance" 2
• Hyperdensity on non-contrast CT (present in only 30% of cases) 2
• "Empty delta sign" on contrast-enhanced images (less commonly seen on CTV than conventional CT) 2

Critical Pitfalls to Avoid

Anatomic variants that can mimic thrombosis:

• Sinus atresia or hypoplasia – particularly common in transverse sinuses 2
• Asymmetrical sinus drainage – normal variant with dominant/hypoplastic pattern 2
• Normal filling defects – arachnoid granulations can appear as filling defects 2
• Flow gaps – less problematic on CTV than time-of-flight MRV 2

Always correlate CTV findings with clinical presentation and non-contrast CT findings, as a negative plain CT does not rule out venous thrombosis. 2

Complementary Imaging

CTV should not be performed as a stand-alone study:

• Non-contrast CT head should precede CTV to assess for hemorrhage, edema, and hyperdense thrombus 1, 2
• MRI/MRV may be needed for problem-solving when CTV is equivocal or to assess parenchymal changes with greater sensitivity 1, 4
• Digital subtraction angiography (DSA) remains gold standard if CTV/MRV are inconclusive or when endovascular intervention is considered 2, 8

Radiation Considerations

• Radiation dose: Moderate (☢☢☢ per ACR classification) 1
• Dose optimization: Use appropriate tube current modulation and limit scan range to necessary coverage 5
• Pediatric protocols: Reduce kVp and mAs according to patient size 1

Clinical Integration

CTV is particularly valuable in emergency settings because:

• Rapid acquisition – typically 5-10 minutes total scan time 5, 8
• Wide availability – accessible 24/7 in most emergency departments 8
• High diagnostic confidence – excellent interobserver agreement reduces need for repeat imaging 7
• Immediate treatment decisions – allows prompt initiation of anticoagulation when thrombosis is confirmed 2, 8