CT head (protocol)

CT head (sometimes termed CT brain), refers to a computed tomography examination of the brain and surrounding cranial structures. It is most commonly performed as a noncontrast study, but the addition of a contrast-enhanced phase is performed for some indications.

This article covers non-contrast and delayed post-contrast imaging. Other specific types of contrast-enhanced CT for cerebrovascular evaluation are discussed separately: CT venography, CT angiography, and CT perfusion.

Indications

The following are common indications for which noncontrast head CT (CT head without intravenous contrast) is usually appropriate ^1,2:

• altered mental status in specific scenarios:
  • known intracranial hemorrhage, mass, infection, or infarct
  • coagulopathy or anticoagulation
  • suspected central nervous system infection
  • suspected elevated intracranial pressure
  • hypertensive emergency
  • acute delirium
  • unknown cause
• cerebrovascular disease in specific scenarios:
  • intracranial hemorrhage suspected or proven
  • dural venous sinus thrombosis suspected
  • ischemic stroke suspected due to focal neurological deficit (new, fixed, or worsening)
  • transient ischemic attack, initial screening
• dementia, initial imaging
• head trauma in specific scenarios:
  • acute head trauma, initial imaging:
    • mild (GCS 13-15) but imaging indicated by clinical decision rule
    • moderate or severe (GCS <13)
    • penetrating trauma
  • acute head trauma, short-term follow-up imaging:
    • positive findings on initial imaging
    • new or progressive neurologic deficits
  • subacute or chronic head trauma with unexplained cognitive or neurologic deficits
  • recent head trauma with suspected cerebrospinal fluid (CSF) leak, initial imaging
  • recent head trauma with acute ataxia
  • pediatric abusive head trauma suspected due to the presence of neurologic signs or symptoms, apnea, complex skull fracture, other fractures, or other injuries highly suspicious for child abuse
• headache in specific scenarios:
  • sudden and severe headache (worst headache of life, thunderclap headache)
  • new headache with papilledema
  • new or worsening headache in the following scenarios:
    • subacute head trauma
    • inciting activity/event such as sexual activity, exertion, or position
    • neurologic deficit
    • known or suspected cancer
    • immunocompromise
    • pregnancy
    • at least 50 years old
• seizures in specific scenarios:
  • epilepsy disorder with change in clinical symptoms or seizure pattern
  • new seizure, initial imaging

Additional indications for noncontrast head CT include the following ²:

• surgery-related indications
  • surgical guidance or preoperative planning
  • postoperative evaluation after intracranial surgery
  • evaluation for CSF shunt malfunction
• skull lesions (such as craniosynostosis, fibrous dysplasia, Paget disease, tumors)
• detection or evaluation of calcification

The administration of intravenous contrast media may improve the sensitivity for detecting brain neoplasms or infections. CT head without and with contrast can be performed as a single non-contrast studyfor these indications if MRI, which is generally superior for these diagnoses, is contraindicated or the combinationunavailable.

Purpose

The purpose of a non-contrast and post-contrast (delayed) studynoncontrast head CT is to evaluate for neurosurgical emergencies with high sensitivity, including acute intracranial hemorrhage, mass effect, territorial infarct, or hydrocephalus. ThisDue to its widespread availability, CT is more often performed than MRI in the acute setting. In addition, CT is superior to MRI for evaluating osseous structures, such as for calvarial or skull base fractures or craniosynostosis.

Contrast-enhanced CT allows the identification of abnormal contrast enhancement (e.g. tumours), such as in brain metastases, some primary brain tumors, and allows enhancement to be differentiated from intrinsic hyperdensity (e.g. blood)brain abscesses. 

Historically, only axial planes were obtained. More recently it has become standard practice to obtain volumetric scans, with subsequent multiplanar reconstructions (see CT head technique).

In addition to various planes, the images can also be reconstructed using different algorithms (e.g. bone algorithm or soft-tissue algorithm) and viewed with different windows(e.g. brain window,subdural window, or bone window) to emphasize various tissue characteristics.