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4.19\ Subdural Drainage Catheters
4.19.1\ Discussion
Chronic subdural hematomas can be treated via burr hole evacuation. The use of drainage catheters that extend through the burr holes from the
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subdural collections to the skin surface can reduce incidence of recurrence. Imaging can be used to confirm the position of catheters and assess changes in size of the hematomas. The hyperattenuating catheters are readily apparent on CT (Fig. 4.47).
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Fig. 4.47 Subdural drainage catheter. Coronal CT images (a, b) show a catheter (arrows) extending from the subdural space to an opening in the scalp
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4.20\ Cranial Surgery
Complications
4.20.1\ Tension Pneumocephalus
Tension pneumocephalus following neurosurgery is an uncommon but emergent condition. Indeed, tension pneumocephalus can be life- threatening since it can cause brainstem herniation. Possible risk factors include posterior fossa craniotomy, the use of nitrogen oxide for anesthesia, lumbar drainage, and cerebrospinal fluid leakage, with dural defects that function as one- way valves.
A characteristic axial CT feature of tension pneumocephalus is the “peaking” sign, in which
the lateral aspects of the bilateral frontal lobes are compressed together by the pressurized intracranial air. Another related appearance is the “Mount Fuji” sign, which describes the combination of compressed and separated frontal lobes with widened interhemispheric space (Fig. 4.48). This sign is fairly specific for tension pneumocephalus.
Ultimately, the diagnosis of tension pneumocephalus requires accompanying decline in clinical status manifesting as lethargy, a hissing noise during release of the pneumocephalus, and resolution of symptoms thereafter. Treatment consists of one or more of the following: 100% oxygen supplementation, repair of dural defect, and burr hole decompression.
Fig. 4.48 Tension pneumocephalus. The patient presented with lethargy on postoperative day #3. Axial CT image obtained after craniotomy shows extensive pneumocephalus that compresses the bilateral frontal lobes and lateral ventricles. There is separation of the frontal lobes and a pointed appearance of the bilateral anterior frontal lobes
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4.20.2\ Entered Frontal Sinus,
Entered Orbit, and Air Leak
The frontal sinus and orbits are entered in about 30% of craniotomies in adults, particularly via the pterional or orbitozygomatic approach. However, these are usually noted during surgery and repair using fat graft and mesh (Figs. 4.49 and 4.50). Superimposed complications are
uncommon and include mucoceles, cerebrospinal fluid leak, and air leak with frontal sinus entry and orbital hematomas and rectus muscle injury with orbital entry. The presence of persistent pneumocephalus or pneumo-orbit on serial CT exams raises the suspicion of air leaks (Fig. 4.51). High-resolution CT with multiplanar reconstructions is the first-line modality recommended for assessing suspected cerebrospinal fluid leaks.
Fig. 4.49 Entered frontal sinus. Axial CT image demonstrates a right frontal craniotomy that extended through the right frontal sinus, which was obliterated with fat graft
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Fig. 4.50 Entered orbit. Coronal CT image (a) shows a defect in the left posterior orbital roof closed with fat graft (arrow). Axial CT image (b) in a different patient shows entry of the left lateral orbit repaired with mesh (arrow)
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Fig. 4.51 Air leak. Axial (a) and coronal (b) CT images show left intraorbital air and proptosis after aneurysm clipping. There is a defect in the superior orbital roof (arrow)
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4.20.3\ Postoperative Hemorrhage |
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craniotomy site and may be caused by separa- |
and Hematomas |
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tion of the dura at the craniotomy margin, sud- |
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den collapse of the brain, or inferior extension |
Small, asymptomatic hematomas are common |
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of regional hemorrhage. |
and can be considered an expected consequence |
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Remote intracranial hemorrhage is a relatively |
of craniotomy and cranioplasty. Subgaleal hema- |
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uncommon complication of intracranial sur- |
tomas are ubiquitous in the early postoperative |
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gery, comprising about 6% of extradural |
period and are usually self-limited. Occasionally, |
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hematomas. This type of hemorrhage may be |
subgaleal hematomas can be voluminous and |
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related to cerebrospinal fluid volume deple- |
exert mass effect (Fig. 4.52). Similarly, postop- |
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tion and decreased intracranial pressure and |
erative intracranial hematomas can occasionally |
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has a predilection for the cerebellum. Remote |
cause symptoms such as altered mental status, |
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cerebellar hemorrhage characteristically |
neurological deficits, and seizures, which may |
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appears as curvilinear high attenuation in the |
require surgical evacuation. The variety of post- |
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cerebellar sulci and folia on CT, which has |
operative hematomas includes epidural (33%), |
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been termed the “zebra sign.” Remote cerebral |
subdural (5%), parenchymal (43%), or a combi- |
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hemorrhages most commonly occur in the |
nation of these (8%) and can be further classified |
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frontal and then followed by the temporal |
as regional, adjacent, or remote (Figs. 4.53, 4.54, |
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lobe. These are most commonly related to the |
4.55, and 4.56). Acute hematomas tend to be |
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use of intraoperative retractors creating |
hyperattenuating on CT, while chronic hemato- |
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venous congestion leading to a hemorrhagic |
mas evolve toward fluid attenuation. |
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venous infarct. Hemorrhagic venous infarcts |
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can also be due to sacrificing crucial venous |
•\ Regional hematomas are the most common |
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and occur directly beneath the bone flaps. |
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Abdominal wall hematomas may result from |
•\ Adjacent extradural hematomas are more |
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storage of calvarial bone flaps for autocranio- |
commonly posterior rather than anterior to the |
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plasty (Fig. 4.57). |
Fig. 4.53 Adjacent epidural hematoma. Axial CT image shows lentiform high-attenuation extradural hematoma (arrow) along the posterior margin of the craniotomy
Fig. 4.52 Subgaleal hematoma. Axial CT image shows a hyperattenuation mass-like collection in the left scalp overlying the craniotomy flap (arrow). There is also a small amount of underlying extra-axial hemorrhage and multiple cerebral infarcts
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Fig. 4.54 Regional subdural hematoma. Axial CT image |
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shows a heterogeneous left subdural hematoma (arrow) |
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Fig. 4.55 Adjacent intraparenchymal hematoma. Preop erative CT image (a) shows a large right frontal convexity meningioma. Immediate postoperative CT image (b) shows a large hyperattenuating hematoma subjacent to the resection cavity. There is also extensive surrounding vasogenic edema
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Fig. 4.56 Remote cerebellar hemorrhage. Axial CT image (a) in a patient who underwent supratentorial craniotomy shows crescentic hemorrhage in the bilateral cerebellar hemispheres. Axial T1-weighted (b), axial T2-weighted (c) and axial susceptibility-weighted (d)
MRI images in a different patient demonstrate curvilinear areas of subacute hemorrhage and edema in the bilateral cerebellar hemisphere (arrows) following left temporal lobe tumor resection (arrowheads)
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Fig. 4.57 Axial CT image shows a large hematoma (*) subjacent to the skull flap within the subcutaneous tissues
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4.20.4\ Postoperative Hygromas
and Effusions
Hygromas develop in up to 60% of cases following craniectomy, particularly decompressive craniectomy for intracranial hypertension related to head trauma. Up to 90% of subdural hygromas are ipsilateral to the craniectomy site. Interhemispheric fissure subdural hygromas are uncommon, as are subarachnoid hygromas. Hygromas can also occur after craniotomy and cranioplasty.
Hygromas usually appear after 1 week of surgery, reach a maximum volume at 3–4 weeks, and resolve over several months. On CT and MRI, hygromas appear as simple fluid collections (Fig. 4.58). However, nearly 8% convert to subdural hematomas by 2 months, resulting in
a
higher attenuation. Most hygromas are of little clinical significance, although some of these may be associated with mass effect that may require additional decompressive surgery.
A particular complication related to posterior fossa tumor resection in pediatric patients is the formation of spinal subdural effusions. These fluid collections result from sudden postoperative normalization of the excessive intraspinal pressure caused by spinal sequestration by tonsillar herniation. On MRI, the effusions display T1 and T2 cerebrospinal fluid signal characteristics, but can also enhance (Fig. 4.59). The collections also tend to have wavy margins and can compress the spinal canal contents, thereby interfering with workup for metastatic disease. Otherwise, the collections are generally clinically silent and resolve within 1 month.
b
Fig. 4.58 Subdural hygroma. Axial T2 (a) and T1 (b) MR images in a different patient show a cerebrospinal fluid intensity collection along the left falx cerebri (arrows)
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Fig. 4.59 Postoperative intraspinal subdural effusions. This pediatric patient underwent recent resection of a posterior fossa medulloblastoma. Sagittal T1-weighted (a, b) and fat-suppressed post-contrast T1-weighted (c, d) MR
images show postoperative findings related to suboccipital cranioplasty and diffuse, but somewhat wavy, enhancing subdural collections that compress the spinal canal contents