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CT/MRI enhancement patterns after cranial surgery /
intervention in children
Poster No.:
C-1433
Congress:
ECR 2015
Type:
Educational Exhibit
Authors:
S. Deftereos, S. Foutzitzi, P. Argyropoulou, P. Prassopoulos;
Alexandroupolis/GR
Keywords:
Pediatric, CT, MR, Diagnostic procedure, Cancer, Cerebrospinal
fluid, Cysts
DOI:
10.1594/ecr2015/C-1433
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Learning objectives
•
•
•
To describe the CT and MR imaging of the postoperative skull and brain in
children.
To illustrate early and delayed postoperative contrast enhancement (CE)
patterns of the postoperative skull and brain in children.
To differentiate the expected and clinically irrelevant enhancement from a
residual pathology and/or from surgical complication.
Normal anatomy. (Fig. 1, 2)
The scalp extends anteroposteriorly from the supraorbital ridge to the superior nuchal line
and laterally to the zygomatic arch and external auditory meatus. The scalp is composed
of five layers:
1.
2.
3.
4.
5.
the skin,
subcutaneous tissue,
galea aponeurotica,
loose areolar connective tissue,
pericranium,
and it contains three primary muscle groups:
1.
2.
3.
frontalis,
occipitalis and
temporalis.
The skull vault, also called calvaria, contains the diploë (Fig. 1) which is a layer of
cancellous bone between the inner and the outer tables of calvaria (cortical bone).
At MR imaging, the inner and outer tables have very low signal intensity, in all sequences.
The appearance of the diploë depends on the age of the patient:
T1-weighted images: low signal intensity (first 2 decades of life) and high signal intensity
thereafter (fatty conversion of the diploic marrow).
The dura mater (a hard double-layered membrane):
•
•
The outer layer is formed by the periosteum (of the inner table of the
calvaria) and
The inner layer is the dura mater proper.
The two layers are continuous except:
at the dural venous sinuses and
Page 2 of 18
at the regions where the inner layer projects inward to form the tentorium cerebelli, the
falx cerebri and cerebelli, and the diaphragm sellae.
On MR images, the dura mater typically appears as low-signal-intensity segments and
it enhances after intravenous contrast material injection (it lacks of blood-brain barrier).
Enhancement typically is most prominent in the segments over the convexities. The two
deeper meningeal layers (arachnoid and pia mater) are not normally visible at imaging
(Fig.2).
Images for this section:
Fig. 1: Normal scalp anatomy [male 6yo]. Axial CT image obtained at the level
of the temporal fossa shows the skin, which appears as a linear hyperattenuating
structure (arrowhead), and subcutaneous tissue, which appears as a thicker layer of
fatty attenuation (thick arrow). The temporalis fascia appears as a thin line of increased
attenuation (straight arrow), and the subgaleal layer of loose areolar tissue contains
fat (curved arrow) and the temporalis muscle (star). Note the inner and outer tables of
calvaria (orbit's level) as well defined and with very high attenuation, as well as the diploic
space with lower attenuation. The galea aponeurotica is a layer of thick fibrous tissue that
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is continuous with the occipitofrontalis and auricularis muscles. The temporalis muscle
lies deep to the temporalis fascia and arises from the temporal fossa pericranium which
is continuous with the galea superiorly. Subgaleal fluid collections can be extensive and
may cross skull sutures (like intracranial subdural fluid collections).
Fig. 2: Normal scalp anatomy [male 5yo]. Axial MR image obtained at the level of Sylvian
fissures. Note the enhancement of pia matter.
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Background
Interpretation of early and/or late postoperative CT and MR imaging following cranial
surgery in children is often cumbersome. Residual pathology or surgical
complications may exhibit contrast enhancement (CE). However, CE related to an
uncomplicated surgery is of no clinical significance.
Complications that are associated with all neurosurgical procedures include infection,
skull fracture, and hemorrhage.
neurosurgical procedures:
burr holes
craniotomy (six standard types [table 1]) - craniectomy - cranioplasty
ventricular shunting.
Images for this section:
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Fig. 4: Table 1. The type of craniotomy is depending to the desired intracranial content
accessibility.
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Findings and procedure details
Burr holes (Fig 4, 5)
Usually complications associated with burr holes is the potential to plunge the drill into
the cranium (less common with with automatic power drills).
T2-weighted MR images may reveal an area of high-signal-intensity oedema underlying
the burr hole (the "mushroom" sign). Haemorrhagic complications of plunging
(intracerebral hematoma, cortical laceration, extradural hematoma, subdural hematoma,
intraventricular hemorrhage) contribute to increased morbidity and mortality and of
course are causes for a prolonged postoperative recovery period. A complication that
may occur in children and particularly in infants is the formation of an enlarging
pseudomeningocele (as a result from a growing burr hole).
Craniotomy
Craniotomy (surgical removal of a portion of the skull). The bone flap is replaced at the
end of the procedure and thereafter is identified according to its location (frontal, bifrontal,
parietal, occipital) (Fig.6).
In the early postoperative period, scalp swelling due to a mixture of oedematous fluid,
hemorrhage, cerebrospinal fluid (CSF), and air, in varying amounts, is common findings.
The swelling typically resolves over several weeks (Fig. 7).
Specific patterns and sites of CE are expected after an uncomplicated cranial surgery
or ventricular shunting (Fig. 12). Enhancement is seen earlier and lasts longer on
MRI than it does on CT. CE may be seen in the traumatized temporalis muscle in the
early postoperative days (pterional craniotomy). Neovascular granulation tissue formed
between the bone flap and the calvaria may enhance within the 1st year after surgery
(Fig. 8, 9). The dura mater enhances in a smooth linear pattern as soon as 9 hours
postoperatively, enhancement can last up to 40 years and almost always occurs in the
portion of the dura mater that is deep to the flap (frequently widespread) (Fig 9). After
brain tissue resection, the surgical margins may begin to enhance within 17 hours (Fig.
10). They initially appear as thin linear areas of enhancement that increase with time# by
the 6th postoperative day they are thicker and nodular. This pattern of brain enhancement
usually resolves within 1 month after surgery (Fig. 11).
Images for this section:
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Fig. 3: Burr hole [boy 14yo]: Bone-dust-packed burr hole in a 14 year-old boy, 1 day
after "drilling".
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Fig. 5: Burr hole (female 13 yo): Axial CT image obtained with both brain and bone
algorithm shows typical burr hole with small amount of air.
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Fig. 6: Bone flap remodeling in a 18-year-old boy 20 months after craniotomy (car
accident). Axial bone algorithm CT image shows the rounded and remodeled margins
of the craniotomy (arrows) and the titanium clamps (arrows) used to hold the left-sided
acrylic flap (thick arrow) in place .
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Fig. 7: Boy 15yo, the early postoperative period, before and after CM reveals scalp
swelling due to a mixture of oedematous fluid, hemorrhage, cerebro¬spinal fluid (CSF),
and air, in varying amounts. The swelling typically resolves over several weeks.
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Fig. 8: Subdural empyema [boy 11 yo] due to unsatisfactory treatment of sinusitis.
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Fig. 9: Same patient with Fig 8: Dural enhancement in 6 months after empyema's
surgical treatment. Axial T1W and axial T1W-gadolinium-enhanced MR images show
smooth enhancement of the thickened left dura mater (compare with the contralateral
dura mater).
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Fig. 10: Haemorragic tumor [girl 9mo] causes hydrocephalus (initial CT). Axial T1W
and axial T1W-gadolinium-enhanced MR images after 1 month of brain tissue resection,
reveal the surgical margins with smooth and somewhat nodular enhancement (arrow).
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Fig. 11: Pylocytic astrocytoma [boy 15yo].Pre-surgical MR and post-surgical MRI in same
level and in axial axial T1W-gadolinium-enhanced MR images after brain tissue resection
(1 month, 7, 27 and 53 monthes), reveal the surgical margins with smooth and somewhat
nodular enhancement resolving gradually after surgery (arrow).
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Fig. 12: Postsurgical (craniopharyngioma) ventricular shunting: Note the enhancement
at the tip of the shunt (xial T1W and axial T1W-gadolinium-enhanced MR images) and
the surround gliosis (T2W image). The findig should not be considered abnormal while
the dura mater is normal. Follow-up MRI (eg after year) is sufficient.
Page 16 of 18
Conclusion
Knowledge of expected CT and MR enhancement patterns after a cranial intervention in
children is fundamental to avoid misinterpretation.
Personal information
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