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*For medical professionals only
Concise and detailed, collect quickly!
Let's talk about the three windows
of the head CT
The structure of various tissues of the human body is different, and the attenuation of X-rays is different, forming different CT values, so different CT values can be used to identify the properties of
tissues.
The absorption of X-ray by air is 0, so the CT value of air is -1000; X-ray attenuation of bone tissue is 2-4 times that of water, with a CT value of +1000; the CT value of water is 0
.
Three windows commonly used for cranial CT (Figures A-C):
- Figure A: The bone window
. - Figure B: The brain window
. - Figure C: The blood window
.
Figure A: Bone window; It is mainly used to identify fractures, sinus cavity lesions, and intracranial pneumoproma
.
Figure B: Brain window; Gray-white matter may be clearly visible, and early signs of stroke or other lesions
leading to cerebral edema may be detected.
Figure C: Blood window; Better for subdural or intracranial hemorrhage
.
This case manifests: bone window display: right parietal bone fracture; All three windows show: soft tissue edema and subcutaneous pneumosum; Blood window: a small amount of subdural hematoma
.
Two common artifact
ray hardening artifacts
should be noted Beam-hardening artefact
Common at the base of the cranial and posterior fossa
.
Volume-averaging artifact
When the layer thickness is large, it can lead to blood density manifestations, which is typical at the base of the brain and tends to occur in the frontal lobe
above the orbit.
This case: cystic lesions of the four ventricles leading to obstructive hydrocephalus
.
Tricranial tomography is commonly used as a baseline
Reid baseline (REL):
- It is the line
from the midpoint of the external auditory canal to the infraorbital margin.
The production of head transverse fault specimens is mostly based on this line, and the baseline of coronal fault specimens is perpendicular to
this line.
Orbital ear line (OML) or canthal ear line (CML):
- It is the connection
between the midpoint of the external auditory canal and the lateral canthus.
Axial cranial scanning (cross-sectional scanning) is mostly based on this line
.
Superior orbital ear line (SML):
- It is the line between the midpoint of the external auditory canal and the midpoint of the supraorbital margin, and the plane through this line is about the same as the plane of the base of the skull, which is conducive to showing the structure of the posterior fossa and reducing skull artifacts
.
Four normal anatomy
1, the level of the ear line of the skull basal canthus
- Bottom of anterior cranial fossa: orbit, eyeball, ethmoid sinus, sphenoid sinus, anterior bed process, etc
.
- Middle cranial fossa: anterior boundary - sphenoid; posterior boundary – petrous temporal bone (petrous bone); inner margin – cavernous sinus and pituitary fossa; Outer margin - temporal bone, with temporal lobe in the fossa and hippocampal gyrus
on the medial side.
- Posterior cranial fossa: anterior margin - petrous; posterior margin - occipital bone; Behind the saddle - the anterior pontine cistern, extending to both sides as the pontine cerebellar angle pool
.
- Fourth ventricle: located on the midline of the posterior fossa, immediately behind the cerebellar vermis, flanked by cerebellar tonsils
.
- Medulla oblongata, pons: located in front of
the fourth ventricle.
2.
Saddle pool level
- Anterior cranial fossa: temporal lobe
.
- Suprasellar pond: above the pituitary fossa, between the two middle cranial fossa, the anterior border is the straight temporal lobe, and the lateral temporal hippocampus, which is pentagram or hexagram star-shaped
.
Its anterior horns are connected to the longitudinal fissure pool, the two lateral corners are connected to the outer fissure pool, the two posterior lateral corners continue to the ring pool, and the sixth corner is located in the middle of the trailing edge, which is the interangular pool
.
The edge of the suprasellar pool is a cerebral artery ring, and a "V" shaped optic chiasm
is often visible in the anterior part of the pool.
- Postcranial fossa: four ventricles or quadrilotic pools
.
3.
The lower level
of the third ventricle shows the lower part of the anterior corner of the lateral ventricle:
- anterior - frontal lobe; lateral - caudate nucleus head; At the posterior midline - the third ventricle, the two sides of which connect the thalamus
.
Postcranial fossa:
- The cerebellar curtain in the shape of a "Y" or "V" shape, with a subenthetular structure on the medial side (supracerebellar vermis) and a supratentorial structure on the lateral side (occipital lobe).
Quad Pool:
- Located in front of
the cerebellar vermis.
4.
The upper level of the third ventricle
- Basal nucleus, thalamus
. - Inner capsule forefoot (forelimb); Between
the caudate nucleus and the legume nucleus. - Internal capsule knee and hindfoot (hindlimb): located between
the legiform nucleus (consisting of the lateral putamen and the medial globus pallidus) and the thalamus. - Lateral to putamen: outer capsule, screen nucleus, outermost capsule, insula (insula).
- Quadruple pool: between the occipital lobes on both sides, there is a pineal gland in the pool, which is anteriorly connected
to the third ventricle.
Basal ganglia (basal nucleus):
- The gray matter nuclei, buried deep in the cerebral hemispheres on both sides, are the main structures
that make up the extrapyramidal system.
Basal ganglia area: conceptual ambiguity
.
May include: basal ganglia, substantia nigra, red nucleus, and surrounding white matter areas
.
- Internal capsule: located in the white matter area between the thalamus, caudate nucleus and legume nucleus, it is densely formed
by upward and descending conduction tracts.
It is divided into three parts: forelimbs, knees, and hindlimbs
.
Cortical brainstem bundles in the knee; The hindlimbs have corticospinal tracts, thalamic cortical tracts, auditory radiation, and optic radiation
. - Outer capsule: is a white matter band located between the screen-like nucleus and the legume-like nucleus, which is mainly composed of
cortical tepal fibers emitted by the insula.
5.
The lateral ventricle body level
is composed of frontal, temporal and occipital lobes, the two lateral ventricles are transparent septum, and the outer side is the caudate nucleus and body part
.
The posterior angle of the lateral ventricle (occipital angle) may be asymmetrical, and calcification
of the choroid plexus is visible in the ventricles.
Longitudinal cirth pools and sickles
of the brain are visible at the midline.
6.
The body of the lateral ventricle is separated by the corpus callosum on the medial wall of the upper level
of the lateral ventricle, the outer part of the lateral ventricle body is the parietal lobe, and the parietal occipital sulcus and the central sulcus treat the brain as the frontal, parietal and occipital lobes
.
7.
The lower level of the cerebral cortex (semi-oval center level)
is above the corpus callosum and lateral ventricles, and the cerebral sickle runs through the midline
from front to back.
The white matter part is the center of semi-oval, the frontal lobe is reduced, the proportion of the parietal lobe is expanded, and the occipital lobe is basically disappeared
.
- Semi-oval center: a myelinated fiber formed by the medulla of the left and right cerebral hemispheres, located above the corpus callosum, symmetrically located in the areas
on both sides of the sickle.
8.
The upper level of the cerebral cortex (the upper level of the semi-oval area)
is close to the top of the skull, the sickle of the brain is clearly visible, and the gray matter and sulci next to it are very clear
.
The parietal lobe is smaller and the frontal lobe is smaller
.
- Radial crown: is the radial fibrous white matter
between the inner capsule and the cerebral cortex.
Five emergency imaging examples
1, skull fracture ▲ frontal bone fracture: fracture
of the inner and outer side wall of the left frontal sinus
。
▲Fracture
of the left temporal bone.
2.
Epidural hematoma ▲ Epidural hematoma, intracranial pneumomata
(indicating fracture).
▲Epidural hematoma (convex lens-like; may or may not have skull fractures).
3.
Subdural hematoma ▲Right subdural hematoma
(acute-high-density, chronic-low-density); Edema of the right side of the brain, displacement
of midline structures.
▲ (subcerebellar enchantery) subdural hematoma
.
▲ (left side of the sickle of the brain) subdural hematoma: mild mass effect
can be seen.
▲Left subdural hematoma: equal density, mass effect, midline structure shifted
.
▲Bilateral subacute subdural hematoma: acute bleeding can be seen on the left side, bilateral mass effect is balanced, and the midline structure is not displaced
.
▲Bilateral isodense subdural hematoma
.
4.
Subarachnoid hemorrhage ▲Traumatic subarachnoid hemorrhage
: high-density shadows
can be seen in the sulci and cistern.
▲Frontal and temporal lobe brain contusion: cerebral hemorrhage with surrounding edema, which can expand over time, resulting in mass effect and cerebral herniation
.
Due to the influence of surrounding bone, contusion at the base of the brain is easy to miss
.
▲ Head gunshot wound: visible bullet trajectory, crossing the midline of the brain, its devastating consequences cause: lateral ventricular hematogram, subarachnoid hemorrhage,
Hydrocephalus (enlargement of the lateral ventricular temporal angle), cerebellar curtain herniation (disappearance or asymmetry of the basal cistern around the brainstem)
▲ Aneurysm rupture leads to subarachnoid hemorrhage, haemapronosis, and non-communicating hydrocephalus
Unlike traumatic subarachnoid hemorrhage, SAH due to aneurysm rupture often does not involve the convex surface of the brain and is located near
the basal cistern.
Cerebral aneurysms are often located in the Willis annular vessels
of the suprasellar pool.
A: quadrivventricular hematogram; B: Mesophore catheter, annular pool, right lateral ventricle temporal angle hemorrhage, anterior communicating artery (aneurysm prone location) bleeding density is high; C: Triventricular hematogram; D-F: lateral ventricular hemorrhage, subarachnoid hemorrhage (blood replaces cerebrospinal fluid).
5.
Hypertensive cerebral hemorrhage Hypertensive cerebral hemorrhage
:
- Spontaneous bleeding;
- secondary to long-term hypertension and chronic vascular disease;
- Common in basal ganglia, thalamus, pons, and cerebellum
.
A: mass effect, adjacent sulci and cistern disappear; F: Cerebral hemorrhage breaks into the four ventricles
.
▲ Hook back hernia: is the result of
the inability of the compensatory mechanism to adapt to the mass lesion.
A large number of hypertensive cerebral hemorrhages in the basal ganglia, breaking into the ventricles and subarachnoid space, surrounding edema, and disappearing the space around the brainstem; Brainstem hemorrhage, hydrocephalus
.
6.
Ischemic stroke of cerebral infarction
- Early: cerebral edema, blurred division of gray-white matter, disappearance of the cerebral sulci;
- Medium-term: reduced density of the lesion area;
- Late stage: Brain parenchyma shrinks in
size.
A: Old cerebral infarction, reduced volume of the right occipital lobe; B: Acute cerebral infarction of the left occipital lobe, blurred gray-white matter demarcation, disappearance of the cerebral sulci;
Another patient: C, D: subacute cerebral infarction, low density, no obvious mass effect
.
▲Cerebral infarction in the blood supply area of the left middle cerebral artery (subacute stage): low density, mild edema
.
The mass effect is most pronounced
at 2 to 4 days of ischemic stroke.
7.
Hydrocephalus
▲ hydrocephalus and ventricular
shunting.
8.
Mass lesions ▲ Most of the symptoms of emergency patients are caused by the mass effect of the lesions
.
Lesions that can cause cerebral edema and mass effect are: primary tumor or metastases, vascular malformations, inflammatory lesions (toxoplasmosis, brain abscess).
This example: the tumor density is high, adjacent to the sickle of the brain, and a large area of low-density edema can
be seen around it.
Part of the content of this article is compiled from Panda Radiology, Medical Neurology Channel, and the wonderful course "Basic Knowledge of Cranial CT and Common Diseases" taught by Director Du Zhigang of Beijing Ditan Hospital at the doctor's station.
Where can I find more clinical knowledge in neurology?
Come to the "Doctor Station" and take a look 👇
