SPIRAL HEAD CT IN THE EVALUATION OF ACUTE INTRACRANIAL PATHOLOGY
HEITOR OKANOBO MD, STEPHEN LEDBETTER MD MPH, AARON SODICKSON MD PhD
EMERGENCY RADIOLOGY, BRIGHAM AND WOMEN’S HOSPITAL, HARVARD MEDICAL SCHOOL, BOSTON, MA
INTRACRANIAL HEMORRHAGE
TECHNIQUE
LEARNING OBJECTIVES:
1. Recognize the benefits of multiplanar reformations
(MPR’s) in the interpretation of head CT.
2. Understand technique differences of spiral head CT, and
potential pitfalls of spiral head CT technique.
BENEFITS OF SPIRAL HEAD CT:
1. As anatomy or pathology is often best demonstrated in an
orthogonal plane, coronal MPR’s often enhance visualization
of structures parallel to the axial plane.1,2
2. MPR’ s add confidence in localization of hemorrhage,
particularly at the vertex, tentorium, or parafalcine.3
Fig 1: a) Typical imaging planes for spiral &
sequential technique. Red lines are straight axial
gantry angle of spiral CT, yellow are gantry angled
parallel to skull base for sequential scan. B) The
head can be tilted forward in patients able to flex
their neck, to eliminate posterior fossa beam
hardening artifact, and to better approximate the
acquisition plane of sequential head CT technique.
Fig 5: Spiral scan a) in a trauma patient
demonstrates either parenchymal of focal
subarachnoid frontal hemorrhage (red). Coronal
MPR b) confirms post-traumatic subarachnoid
hemorrhage confined to the sulcus (yellow).
Fig 6: Spiral scan a) demonstrates subtle parafalcine
hyperdensity (red), possibly subarachnoid or subdural
hemorrhage, vs thickened dura or meningioma. Coronal MPR b)
reveals acute angulation and extension into adjacent sulcus
(yellow), confirming subarachnoid hemorrhage.
Fig 7: Spiral scan a) demonstrates thin subdural
hematoma (red). Coronal MPR b) better depicts
anatomic extent over the vertex (yellow), permits
more accurate measurement of thickness, and
reveals associated effacement of parietal sulci.
Fig 8: Spiral scan a) reveals tentorial
hyperdensity (red) suspicious for subdural
hematoma. Coronal MPR b) shows the
hematoma (blue) to better advantage by depicting
the tentorium in an orthogonal plane.
3. MPR’s may better depict calvarial fractures.4
4. A single spiral acquisition of the head often allows
retrospective reconstruction of maxillofacial images, and may
eliminate the need for repeat scanning.5,6
PITFALLS:
Most CT gantries cannot be tilted for a spiral scan, and
remain perpendicular to the table, resulting in:
1. More frequent inclusion of the skull base and dental
hardware. To avoid this, the head can be tilted (in nontrauma) or the posterior fossa scanned sequentially.
Fig 2: Dental hardware artifact obscures the
posterior fossa in spiral scan a). Repeat sequential
scan b) through the posterior fossa with a tilted
gantry angle eliminates the artifact.
2. Lesions may change position relative to a sequential scan
(similar to axial MRI). Axial-oblique MPR’s parallel to the
skull base can reproduce sequential positioning.
Fig 9: Spiral scan in a trauma patient a) reveals right
frontal scalp laceration (green), and small right
parafalcine hyperdensity (red), either a small subdural
hematoma or a meningioma. On coronal MPR b), the
lesion has a smooth, rounded contour with a broad
dural base, suggesting meningioma. MRI (not shown)
confirmed a homogeneously enhancing lesion with a
dural tail consistent with meningioma.
Fig 10: Spiral CT in a trauma patient a)
demonstrates rounded hyperdensity (red) at
the right parietal convexity, suggesting
subdural hematoma. Coronal MPR b) reveals
adjacent hyperostosis (yellow) of the inner
calvarial table consistent with meningioma.
Fig 11: Spiral scan a) in a patient with prior
glioblastoma multiforme resection reveals
unchanged post-operative subdural collection
(green, prior imaging not shown), and diffuse white
matter hypodensity crossing midline (red). Coronal
MPR b) shows extension across the corpus
callosum (yellow), confirmed on subsequent MRI
(not shown) to represent interval tumor extension.
Fig 12: Spiral scan for trauma identifies infarction
as the likely cause of the patient's fall. Axial image
a) suggests subtle loss of grey-white differentiation
(red), versus asymmetric positioning or volume
averaging. Coronal MPR b) confirms early
infarction (yellow), with loss of grey-white
differentiation, and sulcal effacement, better seen
in cross-section to the anatomy.
SKULL AND MAXILLOFACIAL
kVp; mAs
Detector config1
Sequential Head
CT
120; 450
24 X 1.2 mm
Pitch
N/A
Rotation time (sec.) 1.0
Gantry angle
Parallel to skull
base
Axials (Thickness x 4.8 X 4.8 mm, Brain
interval)
& Bone algorithm
MPR’s (Thickness x N/A
interval)
CTDI 2 mean
63.8
(range)
(59.44 – 69.41)
DLP 2 mean
1044.18
(range)
(1224 – 892)
Spiral Head CT
140; 280 or 120; 400
20 X 0.6 mm
0.75
1.0
True axial to table
5.0 X 5.0 mm, Brain
& Bone algorithm
Routine coronal:
5X5 Brain algorithm
66.01
(64.39 - 67.75)
1247.6
(1649 – 1022)
Table 1: Sequential & Spiral head CT protocol technical parameters
1 Based
on detector configuration options on Siemens Somatom Sensation 64
2 CTDI = CT Dose Index, DLP = Dose Length Product (from the included cases)
Fig 3: Apparent change in hematoma position from
spiral a) & sequential b) scans due to different
acquisition angle. Spiral scans can be reformatted
to angled axial-oblique MPR’s parallel to the skull
base to simulate sequential positioning.
HERNIATION
Fig 14: Coronal MPR
demonstrates parietal
fracture (red) and
diastasis (yellow) of the
lambdoid suture a). We
would like to offer you a
job if you could have
found the fracture
prospectively on the
axial image b).
Fig 13: Spiral scan a) reveals posterolateral maxillary sinus wall fracture
(red), and segmental zygomatic arch
fractures (yellow). Spiral acquisition
enabled retrospective MPR’s without
the need to bring the patient back for a
dedicated maxillofacial scan. Sagittal
MPR b) shows clinically unsuspected
right orbital floor fracture (blue) not
previously detected on axial images.
Fig 15: Spiral scan after
transphenoidal pituitary
adenoma resection a). Sella
turcica evaluation is often
limited in the axial plane,
although an amorphous
hypodensity is present in the
sella (red). Sagittal MPR b)
depicts the bony defect (yellow)
in the sella floor and sphenoid
sinus fat packing.
CONCLUSION
Spiral CT technique enables routine use of high quality MPR’s, and has become our standard approach for all head trauma patients. Improved evaluation of intracranial hemorrhage, mass effect, skull and
maxillofacial fractures are among its many benefits. Although one must be aware of potential technical limitations (e.g. streak artifact in the posterior fossa) and interpretational pitfalls (e.g., apparent change
in location of lesions) when using spiral technique, its routine use in head trauma patients can increase visual conspicuity, diagnostic confidence and interpretational accuracy. In select patients, it can also
reduce radiation exposure and provide for more efficient and timely provision of patient care.
Fig 4: Spiral scan a) of right hemispheric subdural
hematoma, with effaced right quadrigeminal plate
cistern (red) and midline shift. Coronal MPR better
depicts isodense subdural hematoma extent (blue),
permits better size measurement, and directly shows
uncus herniation over the tentorium (green).
REFERENCES
1. Mirvis SE, Shanmuganagthan K. Imaging hemidiaphragmatic injury. Eur Radiol 2007; 17:1411-1421.
2. Jayashankar A, Udayasankar U, Sebastian S, et al. MDCT of thoraco-abdominal trauma: an evaluation of the success and limitations of primary interpretation using MPR’s vs axial images. Emerg Radiol 2008; 15:29-34.
3. Strub WM, Leach JL, Tomsick T, Vagal A. Overnight preliminary head CT interpretations provided by residents: locations of misidentified intracranial hemorrhage. AJNR Am J Neuroradiol 2007; 28:1679-1682.
4. Hofman PA, Nelemans P, Kemerink GJ, Wilmink JT. Value of radiological diagnosis of skull fracture in the management of mild head injury: meta-analysis. J Neurol Neurosurg Psychiatry 2000; 68:416-422.
5. Turner BG, Rhea JT, Thrall JH, Small AB, Novelline RA. Trends in the use of CT and radiography in the evaluation of facial trauma, 1992-2002: implications for current costs. AJR Am J Roentgenol 2004; 183:751-754.
6. Ptak T, Rhea JT, Novelline RA. Radiation dose is reduced with a single-pass whole-body MDCT trauma protocol compared with a conventional segmented method: initial experience. Radiology 2003; 229:902-905.0