Computed tomography of the head
|Computed tomography of the head|
Computer tomography of human brain, from base of the skull to top. Taken with intravenous contrast medium.
|OPS-301 code||3-200, 3-220|
Computed tomography (CT) of the head or Computed Axial Tomography (CAT) scanning uses a series of x-rays of the head taken from many different directions. Typically used for quickly viewing brain injuries, CT scanning uses a computer program that performs a numerical integral calculation (the inverse Radon transform) on the measured x-ray series to estimate how much of an x-ray beam is absorbed in a small volume of the brain. Typically the information is presented as a series of cross sections of the brain.
In approximation, the denser a material is, the whiter a volume of it will appear on the scan, just as in the more familiar "flat" X-rays, where dense bone appears white. CT scans are primarily used for evaluating swelling from tissue damage in the brain, bleeding, and in assessment of ventricle size. Modern CT scanning can provide reasonably good images in a matter of minutes. A spiral CT scan of the head may be performed in 10–30 seconds, making it a good option for children and adults with difficulty holding still for longer periods. The use of contrast dye in CT angiography provides good visualization of the vascular structures and leaks in the blood vessels.
Computed tomography (CT) has become the diagnostic modality of choice for head trauma due to its accuracy, reliability, safety, and wide availability. The changes in microcirculation, impaired auto-regulation, cerebral edema, and axonal injury start as soon as head injury occurs and manifest as clinical, biochemical, and radiological changes. Proper therapeutic management of brain injury is based on correct diagnosis and appreciation of the temporal course of the disease process. CT scan detects and precisely localizes the intracranial hematomas, brain contusions, edema and foreign bodies. Because of the widespread availability of CT, there is reduction in arteriography, surgical intervention and skull radiography.
Even in emergency situations, when a head injury is minor as determined by a physician's evaluation and based on established guidelines, CT of the head should be avoided for adults and delayed pending clinical observation in the emergency department for children. Many people visit emergency departments for minor head injuries. CT scans of the head can confirm a diagnosis of skull fracture or brain bleeding, but even in the emergency room such things are uncommon and not minor injuries so CT of the head is usually not necessary. Clinical trials have shown the efficacy and safety of using CT of the head in emergency settings only when indicated, which would be at the indication of evidence-based guidelines following the physical examination and a review of the patient's history.
Concussion is not an indication for having brain CT or brain MRI and can be diagnosed in the clinic. People with concussion usually do not have relevant abnormalities about which brain imaging could give insight, and so brain imaging should not routinely be ordered for people with concussion. If there is concern about a skull fracture, neurological symptoms in addition to concussion, or other neurological findings including intracranial hemorrhage, then CT imaging may be useful. MRI may be useful for people whose symptoms worsen over time or when structural pathology is suspected.
CT of the head is sometimes used for patients who have sudden hearing loss. This use is not indicated and offers no information which would improve the initial management of the patient. In patients for which there are not other neurological findings, a history of trauma, or a history of ear disease, CT scans should not be used in response to sudden hearing loss.
Special views focusing on the orbit of the eye may be taken to investigate concerns relating to the eye. CT scans are used by physicians specializing in treating the eye (ophthalmologists) to detect foreign bodies (especially metallic objects), fractures, abscesses, cellulitis, sinusitis, bleeding within the skull (intracranial bleeding), proptosis, Graves disease changes in the eye, and evaluation of the orbital apex and cavernous sinus.
Comparison with MRI
Magnetic resonance imaging (MRI) of the head provides superior information as compared to CT scans when seeking information about headache to confirm a diagnosis of neoplasm, vascular disease, posterior cranial fossa lesions, cervicomedullary lesions, or intracranial pressure disorders. It also does not carry the risks of exposing the patient to ionizing radiation. CT scans may be used to diagnose headache when neuroimaging is indicated and MRI is not available, or in emergency settings when hemorrhage, stroke, or traumatic brain injury are suspected.
Several different views of the head are available, including axial, coronal, reformatted coronal, and reformatted sagittal images. However, coronal images require the patient hyperextend their neck, which must be avoided if any possibility of neck injury exists.
|Wikimedia Commons has media related to Computed tomography images of the brain.|
- Filler, Aaron (12 July 2009). "The History, Development and Impact of Computed Imaging in Neurological Diagnosis and Neurosurgery: CT, MRI, and DTI". Nature Precedings. doi:10.1038/npre.2009.3267.5.
- Malcolm Jeeves (1994). Mind Fields: Reflections on the Science of Mind and Brain. Grand Rapids, MI: Baker Books., p. 21
- Kunimoto, Derek; Kunal Kanitkar; Mary Makar (2004). The Wills eye manual: office and emergency room diagnosis and treatment of eye disease. (4th ed.). Philadelphia, PA: Lippincott Williams & Wilkins. pp. 360–361. ISBN 978-0781742078.
- Gupta, Prashant; Krishna Atul; Dwivedi Amit; Gupta Kumkum; Bala Madhu; Garg Gouri; Agarwal Shivani (October–December 2011). "CT Scan Findings and Outcomes of Head Injury Patients: A Cross Sectional Study". Journal of Pakistan Medical Students 1 (3). Retrieved 1 December 2012.
- American College of Emergency Physicians, "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American College of Emergency Physicians), retrieved January 24, 2014, which cites
- Jagoda, Andy S.; Bazarian, Jeffrey J.; Bruns, John J.; Cantrill, Stephen V.; Gean, Alisa D.; Howard, Patricia Kunz; Ghajar, Jamshid; Riggio, Silvana; Wright, David W.; Wears, Robert L.; Bakshy, Aric; Burgess, Paula; Wald, Marlena M.; Whitson, Rhonda R. (2008). "Clinical Policy: Neuroimaging and Decisionmaking in Adult Mild Traumatic Brain Injury in the Acute Setting". Annals of Emergency Medicine 52 (6): 714–748. doi:10.1016/j.annemergmed.2008.08.021. ISSN 0196-0644.
- Stiell, Ian G. (2005). "Comparison of the Canadian CT Head Rule and the New Orleans Criteria in Patients With Minor Head Injury". JAMA 294 (12): 1511. doi:10.1001/jama.294.12.1511. ISSN 0098-7484.
- Haydel, Micelle J.; Preston, Charles A.; Mills, Trevor J.; Luber, Samuel; Blaudeau, Erick; DeBlieux, Peter M.C. (2000). "Indications for Computed Tomography in Patients with Minor Head Injury". New England Journal of Medicine 343 (2): 100–105. doi:10.1056/NEJM200007133430204. ISSN 0028-4793. PMID 10891517.
- Smits, Marion (2005). "External Validation of the Canadian CT Head Rule and the New Orleans Criteria for CT Scanning in Patients With Minor Head Injury". JAMA 294 (12): 1519. doi:10.1001/jama.294.12.1519. ISSN 0098-7484.
- American Medical Society for Sports Medicine (24 April 2014), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American Association of Blood Banks), retrieved 29 July 2014, which cites
- McCrory, P; Meeuwisse, WH; Aubry, M; Cantu, B; Dvorák, J; Echemendia, RJ; Engebretsen, L; Johnston, K; Kutcher, JS; Raftery, M; Sills, A; Benson, BW; Davis, GA; Ellenbogen, RG; Guskiewicz, K; Herring, SA; Iverson, GL; Jordan, BD; Kissick, J; McCrea, M; McIntosh, AS; Maddocks, D; Makdissi, M; Purcell, L; Putukian, M; Schneider, K; Tator, CH; Turner, M (Apr 2013). "Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012.". British journal of sports medicine 47 (5): 250–8. PMID 23479479.
- American Academy of Otolaryngology – Head and Neck Surgery, "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American Academy of Otolaryngology – Head and Neck Surgery), retrieved August 1, 2013, which cites
- Stachler, R. J.; Chandrasekhar, S. S.; Archer, S. M.; Rosenfeld, R. M.; Schwartz, S. R.; Barrs, D. M.; Brown, S. R.; Fife, T. D.; Ford, P.; Ganiats, T. G.; Hollingsworth, D. B.; Lewandowski, C. A.; Montano, J. J.; Saunders, J. E.; Tucci, D. L.; Valente, M.; Warren, B. E.; Yaremchuk, K. L.; Robertson, P. J.; American Academy of Otolaryngology-Head Neck Surgery (2012). "Clinical Practice Guideline: Sudden Hearing Loss". Otolaryngology -- Head and Neck Surgery 146 (3 Suppl): S1–35. doi:10.1177/0194599812436449. PMID 22383545.
- American Headache Society (September 2013), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation (American Headache Society), retrieved 10 December 2013, which cites
- Health Quality, O. (2010). "Neuroimaging for the evaluation of chronic headaches: An evidence-based analysis". Ontario health technology assessment series 10 (26): 1–57. PMC 3377587. PMID 23074404.
- Evans, R. W. (2009). "Diagnostic Testing for Migraine and Other Primary Headaches". Neurologic Clinics 27 (2): 393–415. doi:10.1016/j.ncl.2008.11.009. PMID 19289222.
- Semelka, R. C.; Armao, D. M.; Elias Jr, J.; Huda, W. (2007). "Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI". Journal of Magnetic Resonance Imaging 25 (5): 900–909. doi:10.1002/jmri.20895. PMID 17457809.
- Brenner, D. J.; Hall, E. J. (2007). "Computed Tomography — an Increasing Source of Radiation Exposure". New England Journal of Medicine 357 (22): 2277–2284. doi:10.1056/NEJMra072149. PMID 18046031.
- Ebel, Klaus-Dietrich; Benz-Bohm, Gabriele (1999). Differential diagnosis in pediatric radiology. Thieme. pp. 538–. ISBN 978-3-13-108131-5. Retrieved 18 July 2011.