CT brain hemorrhage

Indication/Technique

Indication:

Common indications for a brain CT without contrast:

  • trauma
  • subarachnoid / intracranial hemorrhage
  • ischemia 
  • hypoxia

Intravenous contrast may be given when there is a suspicion of:

  • aneurysm 
  • sinus thrombosis
  • tumor/metastases

Technique:

In a standard scan, the patient is lying with his or her back to the table. 
Depending on the scanner, transversal images may be reconstructed in the coronal plane and sagittal plane. When desired, intravenous contrast may be administered to obtain a CT angiogram (= CTA). 
The CT technique uses Hounsfield units (fig. 1). Read the X ray/CT Technique class (under Basic knowledge) for more information on Hounsfield units.

Figure 1. Hounsfield unit (HU) scale.

Normal anatomy

Brain parenchyma

The brain surface consists of gyri (ridges) and sulci (grooves). In brain edema, the sulci will be compressed, as opposed to atrophy (as in Alzheimer's disease); here the sulci will expand as a result of tissue loss. 
The gray matter is at the outside of the brain parenchyma. Gray matter is somewhat denser on CT than white matter. This is because white matter (as opposed to gray matter) contains the fatty substance myelin (fig. 2/3).

Figure 2. Hounsfield unit (HU) scale.

 Figure 3. Normal brain anatomy in the transversal plane.

Brain lobes

The two hemispheres are subdivided into four lobes: the frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe (fig. 4).
The frontal and parietal lobes are separated by a deep groove, the central sulcus (= Rolando’s fissure). The Sylvian fissure (= lateral fissure) separates the frontal lobe from the temporal lobe.

Figure 4. Brain lobes.

Meninges

The brain is covered from inside out by the pia mater, the arachnoid mater, the dura mater and the skull roof (fig. 5).

Figure 5. Normal anatomy of the cerebral meninges.

The physiologic subarachnoid space consists of a fine web of collagen/elastic fibers and is located between the pia mater and arachnoid mater. In this space are blood vessels and the cerebrospinal fluid.
A venous hemorrhage may cause an artificial subdural space between the arachnoid mater and dura mater (see subdural hematoma in Pathology section).
The outer layer of the dura mater is attached to the skull roof. The inner layer of the dura mater has deep folds (= dural folds) into the skull; the cerebral falx and cerebellar tentorium (fig. 5).
 

Ventricular system

Cerebrospinal fluid, often abbreviated as CSF, is produced in the choroid plexus, located in the ventricles. The CSF circulates from the ventricles (through the 3rd ventricle & the aqueduct) to the 4th ventricle. The CSF then flows through the foramina to the subarachnoid space over the convexity of the brain and around the spinal cord (fig. 6). Resorption takes place in the venous sinus (through the arachnoid granulation, fig 7).
The CSF acts as a transport medium of nutrients and waste and as a cushion for the brain and spinal cord.

Figure 6. Circulation of the cerebrospinal fluid in the coronal plane (a) and sagittal plane (b).

Figure 7. Resorption of CSF through the arachnoid granulation in the venous sinus.

Subarachnoid cisterns

The subarachnoid space is enlarged in certain places; the subarachnoid cisterns. These spaces are filled with CSF and in some places also surround arteries/veins/cranial nerves.

A few important subarachnoid cisterns include (fig. 8 - 11):

  • Sylvian fissure; space between the temporal and frontal lobes.
  • quadrigeminal cistern (transversal W shape). 
  • suprasellar cisterns (transversal pentagon/5-sided shape). 
  • prepontine cisterns (transversal moon shape). 
  • cisterna magna (cerebellomedularis); caudal of the cerebellum and dorsal of the medulla oblongata.

Figure 8. Overview of a number of important subarachnoid cisterns in the sagittal plane.

 Figure 9. Sylvian fissure and quadrigeminal cistern (W shape) in the transversal plane.

 Figure 10. Suprasellar cistern (pentagon) in the transversal plane.

 Figure 11. Prepontine cisterns (moon shape) in the transversal plane. Fourth ventricle (IV).

Checklist

The following points can be used as a guide to assess a brain CT to demonstrate/exclude a hemorrhage. 

1.    Brain parenchyma:

  • is there asymmetry anywhere or obliteration of the gyri sulci pattern? 
  • abnormal gray-white matter differentiation?  
  • hypo/hyperdense abnormalities? 

2.    Hemorrhage:

  • type/cause/location? 
  • subarachnoid cisterns; obliteration of the W shape, pentagon, moon shape, Sylvian fissure? 
  • mass effect or signs of herniation?  is there still space around the brain stem?

3.    Ventricular system:

  • hydrocephalus? 
  • intraventricular blood? 

4.    Bone:

  • extracranial soft tissue swelling?  
  • fracture? Pneumocephalus? 
  • normal air content of the sinuses and the mastoid?  Air-fluid (blood) levels in the sinus? (CAUTION: fracture!)

5.    Old examinations:

  • new findings?

Pathology

  • Subarachnoid hemorrhage
  • Subdural hematoma
  • Epidural hematoma
  • Parenchymal hemorrhage
  • Complications of hemorrhages 

Subarachnoid hemorrhage:

In a subarachnoid hemorrhage, the blood is located in the subarachnoid spaces (fig. 12). The subarachnoid spaces include the basal cisterns (= space around the brain stem), the Sylvian fissure, the cerebral sulci, the intraventricular space and the interhemispheric fissure (fig.13).

Figure 12. Detailed illustration of a subarachnoid hemorrhage. The blood is located between the pia mater and the arachnoid mater.

Figure 13. Brain in the coronal plane. The subarachnoid hemorrhage follows the gyri sulci pattern and spreads out over the left convexity.

The hemorrhage may be secondary to a head trauma. Atraumatic subarachnoid blood is usually the result of a cerebral aneurysm (75%-80%). Other non-traumatic causes include: an AV malformation, eclampsia and hypertensive hemorrhage.
Patients generally present with acute headache (‘worst headache ever').

A CT examination without contrast is the first diagnostic choice. Additionally, a CT angiogram (= CTA) of the brain can be made to detect e.g. an intracranial aneurysm.
        
Characteristic on a CT without contrast (fig 14-16):

  • subarachnoid blood in the basal cisterns, Sylvian fissure and along the cerebral convexity.  
  • intraventricular blood with possibly a blood-fluid level in the posterior horn of the lateral ventricle.  

 Figure 14. Subarachnoid blood in the prepontine cisterns (hyperdense obliteration of the moon shape).

 Figure 15. Blood along the right cerebral convexity. The blood follows the cortical gyri sulci pattern, characteristic of subarachnoid blood.

 Figure 16. Extensive intraventricular blood in the left lateral ventricle, the aqueduct and the 4th ventricle.

Complications of subarachnoid hemorrhage (see also Complications of hemorrhages section):

  • hydrocephalus.
  • ischemia secondary to vasospasm (4-10th day in particular).
  • recurrent hemorrhage. 

Comment:
The sensitivity of the CT depends on the amount of blood and the time of scanning. The first 48 hours have good sensitivity to detect subarachnoid blood.  Sensitivity then diminishes rapidly (< 50% after 1 week). This is due to the relatively quick resorption of the subarachnoid blood.

Subdural hematoma 

The blood is located between the dura mater and the arachnoid mater. 
In 70-80% of the cases this is caused by a venous hemorrhage from ruptured venous anastomoses; in 20-30% the cause is arterial (fig.17/18).

Figure 17. Detailed illustration of a subdural hemorrhage in a ruptured venous anastomosis. The blood is located between the dura mater and the arachnoid mater.

Figure 18. Brain in the coronal plane. Subdural hematoma along the left convexity.

Patients may present with symptoms of headache, reduced consciousness and/or abnormal pupils. 
In young people this is often caused by trauma. The elderly need not always have had severe head trauma.  Note: the cortical veins in the elderly are more ‘stretched’ due to brain atrophy. This promotes the development of a ruptured vein.
A sickle-shaped rind is generally seen on a CT scan along the cerebral convexity (fig. 19).
The aspect of a subdural hematoma on a CT may vary: from hyperdense/heterogeneous in the acute phase to iso/hypodense during the chronic phase. In a mixed picture, fresh hemorrhages are seen in a chronic subdural hematoma.

 Figure 19. Chronic subdural hematoma (= hypodense) at right with an acute bleeding component (= hyperdense).

When the hemorrhage is small, the abnormality on CT scan may be very subtle. Therefore you should always look for asymmetries and the presence of an obliterated gyri sulci pattern.
 

Epidural hematoma

The blood is located between the inside of the bone and the dura mater. An epidural hematoma is an arterial hemorrhage and is strongly associated with a skull fracture (fig. 20).

Figure 20. Detailed illustration of an epidural hemorrhage and a skull fracture. The blood is located between the inside of the bone and the dura mater.

Figure 21. Brain in the coronal plane. Epidural hematoma along the left convexity.

As opposed to subdural hematoma, a lens-shaped rind is seen in an epidural hematoma. 
Characteristically, the hemorrhage is limited to the skull sutures. A cross-over of a suture is possible only when the fracture has caused a diastasis of a suture. 
Depending on size, mass effect and the clinical situation, either surgical intervention or conservative strategy is opted for.

 Figure 22. Left temporal epidural hematoma with a comminuted fracture of the temporal bone & multiple facial fractures (brain CT without contrast in brain setting & bone setting).

Intracerebral hemorrhage

Refers to a bleeding in the brain parenchyma, also known as intra-axial hemorrhage. There are various types of intracerebral hemorrhages (see also fig. 23/24).
Trauma is the most common cause. Below is a list of atraumatic intraparenchymal hemorrhages:

Elderly:

  • hypertension
  • amyloid angiopathy
  • hemorrhagic transformation of an ischemic infarction
  • hemorrhagic tumor
  • coagulopathy

Young adults:

  • vascular anomaly (includes AV malformation, aneurysm) 
  • venous sinus thrombosis  
  • vasculitis
  • hemorrhagic encephalitis
  • cavernoma

A sharply delineated hyperdensity is seen on the CT without contrast (HU around +40, consistent with blood), see also figure 23/24. Depending on location and extent, the hemorrhage may spread into the ventricular system. 
It is particularly important to differentiate between a primary hemorrhage and a hemorrhage caused by an underlying lesion, e.g. a tumor. 

 Figure 23. A 60-year-old patient familiar with hypertension. The CT without contrast reveals a right-sided intraparenchymal hemorrhage in the basal ganglia. In view of location (and patient history), this is most likely a hypertensive hemorrhage.

 Figure 24. Multiple hemorrhagic brain metastases with surrounding (vasogenic) edema. The patient turned out to have a history of melanoma on his back.

Complications of hemorrhages

Cerebral herniation
The intracranial content consists for 80% of brain, 10% blood and 10% cerebrospinal fluid. The mean intracranial pressure (ICP) is 10 mmHg. Because a bleeding, tumor or edema takes up space, pressure may increase. Symptoms such as headaches, nausea and vomiting may develop. 
A local abnormality may cause mass effect and displacement of brain parenchyma. When the median brain structures cross the midline (= imaginary separation line between the two hemispheres), the term midline shift is used (fig.  25).

 Figure 25. Midline shift towards left in a right-sided subdural hematoma (chronic subdural hematoma with an acute bleeding component).

Cerebral herniation occurs when the brain is displaced under the cerebral falx, the cerebellar tentorium or through the foramen magnum, causing loss of brain stem functions (fig. 26).
Various types of cerebral herniations in supratentorial mass effect:

  1. subfalcine herniation (cingulate herniation): displacement of brain tissue under the cerebral falx.   
  2. uncal herniation (downward transtentorial herniation): the medial part of the temporal lobe is pushed down towards the cerebellum.  
  3. transforaminal herniation: downward displacement and herniation of the cerebellar tonsils at the level of the foramen magnum.  
  4. external herniation: displacement of brain tissue to the exterior. Can be seen in a skull fracture or after a craniotomy.   
     

Cerebral herniations may lead to occlusion of blood vessels, hemorrhagic infarctions and edema, adding to the mass effect.

Figure 26. Various types of cerebral herniations in supratentorial mass effect. M = mass effect, e.g. secondary to hemorrhage or a tumor.

 Figure 27. Subfalcial herniation, midline shift and uncal herniation secondary to large subdural hematoma in the left hemisphere.

Hydrocephalus
Enlargement of the ventricles may also occur in generalized atrophy; ex-vacuo dilatation of the ventricles (fig. 28).

Figure 28. Enlarged sulci with tissue loss (atrophy) and concomitant ex-vacuo dilatation of the ventricles.

Another cause of increased volume of the ventricular system is hydrocephalus. Hydrocephalus can be subdivided into communicating and non-communicating hydrocephalus.
In communicating hydrocephalus, the CSF can leave the ventricles; e.g. in reduced CSF resorption, increased CSF production and normal pressure hydrocephalus (NPH).  In non-communicating hydrocephalus, the CSF cannot leave the ventricles; e.g. in aqueduct stenosis, intra ventricular hemorrhage, obstruction secondary to a tumor.

Sources

  • D. M. Yousem et al; The Requisites – Neuroradiology (2010)
  • J. B. M. Kuks,J.W. Snoek; Klinische neurologie (2007)
  • M. Schünke, E.Schulte, U.Schumacher; Anatomische atlas Prometheus: Hoofd, hals en neuroanatomie (2007)
  • A.D. Perron et al; A multicenter study to improve emergency medicine residents' recognition of intracranial emergencies on computed tomography. Ann Emerg Med. 1998.
  • M. Prokop et al; Spiral and Multislice Computed Tomography of the body (2003)

Author

  • Annelies van der Plas, resident radiology LUMC

09/03/2014 (translated: 12/09/2016)

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