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01.NEU.0000367722.66098.21

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CLINICAL STUDIES
Determining the Sensitivity of Computed
Tomography Scanning in Early Detection of
Subarachnoid Hemorrhage
OBJECTIVE: This study aims to determine the sensitivity of modern computed tomography (CT) scanners in detecting subarachnoid hemorrhage (SAH) and to determine whether
there is a continued need for lumbar puncture to exclude the diagnosis.
METHODS: This retrospective study was conducted from January 2000 to December 2005.
The study population consisted of all patients referred on suspicion of SAH or with verified SAH. All medical records were reviewed together with results from CT scan, angiography, and cerebral spinal fluid analysis. Clinical history, examination findings, and time from
onset of symptoms until CT scan (days) were recorded. Patients with a negative CT scan
had a lumbar puncture done.
RESULTS: A total of 499 patients were included. In 203 patients the diagnosis was excluded
by a negative CT scan and negative lumbar puncture. Two hundred ninety-six patients
were found to have a SAH. The diagnosis in 295 of these patients was based on a positive
CT scan. In a single patient, on day 6, the diagnosis was based on a positive lumbar puncture. From day 1 to day 5, CT scanning was found to have a sensitivity of 100%. Overall, CT
scanning had a sensitivity of 99.7 % (95% confidence interval: 98.1–99.99% ).
CONCLUSION: CT scanning is excellent for diagnosing SAH. We demonstrate that in the
first days after ictus a negative CT scan is sufficient to exclude SAH. Data do not allow for
any specific cutoff point to be made. We suggest leaving out lumbar puncture in the first
3 days after ictus if the results of the CT scan are negative.
Søren Cortnum, MD
Department of Neurosurgery,
Aalborg Hospital,
Aarhus Universityhospital,
Aalborg, Denmark
Preben Sørensen, MD
Department of Neurosurgery,
Aalborg Hospital,
Aarhus Universityhospital,
Aalborg, Denmark
Jesper Jørgensen, MD
Department of Neurosurgery,
Aalborg Hospital,
Aarhus Universityhospital,
Aalborg, Denmark
Reprint requests:
Søren Cortnum, MD,
Department of Neurosurgery, Aalborg
Hospital, Aarhus Universityhospital,
Ny Kastetvej 32, 15. 9000 Aalborg,
Denmark.
E-mail: cortnumx@hotmail.com
KEY WORDS: CT scanning, Lumbar puncture, Subarachnoid hemorrhage
Received, February 15, 2009.
Neurosurgery 66:900-903, 2010
DOI: 10.1227/01. NEU.0000367722.66098.21
www.neurosurgery-online.com
Accepted, October 17, 2009.
Copyright © 2010 by the
Congress of Neurological Surgeons
A
neurysmal subarachnoid hemorrhage (SAH)
is a potentially devastating disease. Patients
who survive the initial hemorrhage are at
high risk of rebleeding, which may result in death
or permanent neurological deficits. Previous studies show that early detection leads to vastly improved outcomes. It is of the utmost importance,
therefore, that an early diagnosis or exclusion of
this disease can be made with a high degree of certainty.1,2
Currently, patients suspected of having a SAH
have a computed tomography (CT) scan of the
head performed. If the CT scan is negative for
SAH, these patients have a lumbar puncture done.
The detection of xanthochromia in the spinal fluid
ABBREVIATIONS: sAVM, spinal arteriovenous malformation; SAH, subarachnoid hemorrhage
900 | VOLUME 66 | NUMBER 5 | MAY 2010
is currently considered to be the gold standard for
diagnosing SAH.3-5
The current guidelines for diagnosing SAH are
mainly based on studies done in the 1980s and
1990s. These studies found that CT scanning had
an unacceptable rate of false negatives in detecting
SAH, and lumbar puncture has therefore remained
mandatory for the exclusion of this disease.6-8
Previous studies quote the sensitivity of CT
scanning at 93 to 95% within the first 24 hours
after onset of symptoms. Three days after onset
of symptoms the sensitivity declined to 85%.
After one week the sensitivity was only 50%.8
In the time since these studies were conducted
the technology behind CT scanning has improved
vastly, and it is possible that the accuracy in detecting SAH has improved accordingly. Today highresolution, multidetector CT scanners are widely
available in most hospitals in Western countries.
www.neurosurgery-online.com
CT SCANNING IN SAH EARLY DETECTION
This retrospective study aims to determine the sensitivity of
modern CT scanners in detecting SAH and to determine whether
there is a continued need for lumbar puncture to exclude the diagnosis. To our knowledge this is the largest study of its kind in
recent years.
MATERIALS AND METHODS
This retrospective study was conducted at the neurosurgical
unit at Aalborg University hospital from January 2000 to December
2005. Aalborg Hospital is a major Danish University hospital covering the northern region of Jutland with a population base of
approximately 750 000 people.
The study population consisted of all patients referred to our
neurosurgical unit on suspicion of SAH or with verified SAH.
The hospital chart database was used to identify all medical
records on these patients. The database was also searched for
patients having a lumbar tap done during hospital stay. All medical records were reviewed by two experienced members of the
neurosurgical staff. The medical records were reviewed together with
CT scan, angiography, and results from cerebral spinal fluid analysis. Clinical history, examination findings, and time from onset
of symptoms until CT scan (days) were recorded.
All patients had a CT scan of the head performed. If the CT
scan was positive for SAH the patients subsequently had angiography studies performed and were allocated to appropriate treatment. Throughout the study period a range of different CT scanners
were used at our institution and referring hospitals. The first multidetector CT scanners were introduced in 1998. Ever since, technological advances have been very rapid. Today’s market standard
is a 64-slice multidetector CT scanner. Reflecting this development, scanners were gradually replaced and upgraded throughout
the study period. All scanners used were considered contemporary
standard equipment at the time.
Patients with a negative CT scan had a lumbar puncture done.
Cerebral spinal fluid was sent to the laboratory for cell counts and
all samples were analyzed for xanthochromia by spectrophotometry. Lumbar punctures were done no earlier than 12 hours after
onset of symptoms.
All complications to lumbar puncture resulting in prolonged
hospitalization or readmission were recorded. All data were compiled in a customized database allowing for later analysis.
RESULTS
During the study period, 510 were admitted. Eight patients
were excluded because no lumbar puncture was performed
because there was no clinical suspicion of SAH. In 2 patients the
CT scan revealed an angioreticuloma (capillary hemangioblastoma according to World Health Organization classification).
These patients were excluded. In 1 patient a spinal hemorrhage
was demonstrated on magnetic resonance imaging. Angiography
studies revealed no vascular abnormalities. This patient was
excluded.
NEUROSURGERY
Four hundred ninety-nine patients were included. In 203 patients
the diagnosis was excluded by a negative CT scan and negative
lumbar puncture. Two hundred ninety-six patients had a SAH. In
295 of these patients the diagnosis was based on a positive CT
scan. In a single patient, on day 6, the diagnosis was based on a
positive lumbar puncture.
From day 1 to day 5 CT scanning had a sensitivity of 100%
and a specificity of 100%. Overall CT scanning had a sensitivity
of 99.7% (95% confidence interval (CI): 98.1–99.99%) and a
specificity of 100% (98.2–100%).
Among those patients who had a lumbar puncture done, 4
patients had a viral meningitis. These patients were transferred to
the infectious diseases unit.
Fifteen patients experienced post dural puncture headaches,
equivalent to 7.4%. Only patients with symptoms severe enough
for readmission or prolonged hospitalization were recorded.
DISCUSSION
The majority of patients presented within the first days after
onset of symptoms with declining numbers on the following
days (see Table 1). This is not surprising given the severity of
the symptoms.
As mentioned above CT scanning was found to have a sensitivity of 100% from day 1 to day 5. With declining patient numbers
on the later days it is not possible to define an exact “cutoff point.”
However, it seems safe to leave out lumbar puncture from day 1
to day 3 if the CT scan is negative. Our numbers suggest that this
even allows for a considerable safety margin. To our knowledge
this is the largest study of its kind in recent years.
A recent study published by Boesiger and Shiber9 supports
these findings, also quoting the sensitivity of fifth-generation CT
scanners evaluating for SAH as 100%. This study is quite small,
however, resulting in a wide 95% CI ranging from 61 to 100%.
Some older studies report less convincing results quoting the
sensitivity of CT scanners from 95% to 97%. Most of these are also
quite small and have not stratified patients according to time from
onset of symptoms until CT scanning. It is well known that the
sensitivity of CT scanners decreases with time from onset of symptoms as mentioned above. Also, some of these studies depended
on older third-generation scanners.6,7,10-13
The finding of 4 patients with a viral meningitis reminds us
that, if there is any clinical suspicion of a neuroinfection, a lumbar puncture should always be done.
Although lumbar puncture is generally safe, complications are
not uncommon. In our study 7.4% of the patients who had a
lumbar puncture done experienced severe post dural headaches.
This figure is probably an underestimate because only patients
with symptoms severe enough for readmission or prolonged hospitalization were recorded. Some studies quote the occurrence of
post dural headaches to be as high as 40%.14
According to generally accepted guidelines a lumbar puncture
should be performed no earlier than 12 hours after onset of symptoms. Apart from patient discomfort due to the procedure, this
VOLUME 66 | NUMBER 5 | MAY 2010 | 901
CORTNUM ET AL.
TABLE 1. Presentation of Symptomsa
Diagnosis
by CT Scan
Diagnosis by
Lumbar Puncture
Negative CT Scan,
Negative Lumbar
Puncture
Total
Sensitivity, %
Specificity. %
243
0
121
364
100
100
2 days
14
0
14
28
100
100
3 days
5
0
17
22
100
100
25
1
29
55
96
100
8
0
22
30
295
1
203
499
99.66
100
<1 day
4-7 days
>1 week
Total
a
CT, computed tomography.
also means that many patients have to be hospitalized overnight,
taking up resources of the hospital staff.
Subarachnoid hemorrhage from spinal arteriovenous malformations (sAVM) could be considered a problem. In the literature
35 cases of intracranial subarachnoid hemorrhage from a sAVM
are described. In all these cases SAH was diagnosed on a CT scan.
Bleeding from sAVM without intracranial extensions of blood will
most likely present with symptoms of back pain, sensory disturbances, and paresis of the extremities.15
As mentioned above it seems to be safe to leave out lumbar
puncture from day 1 to day 3 if the results of the CT scan are negative. The CT images should always be evaluated by either a neurosurgeon or a dedicated neuroradiologist if the diagnosis is to be
excluded without doing a lumbar puncture. This algorithm should
therefore only be used in specialized centers. Patients arriving to
hospital later than day 3 should always have a lumbar puncture done
if the results of the CT scan are negative. Previous studies show that
even the sensitivity of lumbar puncture decreases after day 14.
After 3 weeks the sensitivity of lumbar puncture has decreased to
70%, and after 4 weeks the sensitivity is only 40%.16 This means
that patients arriving later than day 14 should be evaluated by
angiography studies.
Since the conclustion of our study, the algorithm outlined above
has been implemented at our institution.
CONCLUSION
CT scanning is excellent for evaluating patients suspected of
having a SAH. We show that CT scanning has a sensitivity of
100% from day 1 to day 5. Because of declining patient numbers
on the later days, it was not possible to establish an exact “cutoff
point.” We suggest leaving out lumbar puncture from day 1 to
day 3 if the CT scan is negative, which allows for a considerable
safety margin.
Overall CT scanning had a sensitivity of 99.7% (95% CI:
98.1–99.99%) and a specificity of 100% (98.2–100%). A lumbar
puncture should always be done if any clinical suspicion of a neuroinfection exists.
902 | VOLUME 66 | NUMBER 5 | MAY 2010
Disclosure
The authors have no personal financial or institutional interest in any of the
drugs, materials, or devices described in this article.
REFERENCES
1. Mayer PL, Awad IA and Todor R, et al. Misdiagnosis of symptomatic cerebral
aneurysm: prevalence and correlation with outcomes at four institutions. Stroke.
1996;27(9):1558-1563.
2. Hop JW, Rinkel GJ, Algra A, van Gijn J. Case fatality rates and functional outcome after subarachnoid hemorrhage: a systematic review. Stroke. 1997;28(3):660664.
3. Wasserberg J, Barlow P. Lesson of the week: lumbar puncture still has an important
role in diagnosing subarachnoid haemorrhage. BMJ. 1997;315(7122):1598-1599.
4. Prosser RL Jr. Feedback: computed tomography for subarachnoid hemorrhage:
which review should we believe regarding the diagnostic power of computed tomography for subarachnoid hemorrhage? Ann Emerg Med. 2001;37(6):679-685.
5. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med. 2000;342(1):29-36.
6. Morgenstern LB, Luna-Gonzales H, Huber JC Jr, et al. Worst headache and subarachnoid hemorrhage: prospective, modern computed tomography and spinal
fluid analysis. Ann Emerg Med. 1998;32(3 pt 1):297-304.
7. Weir B. Headaches from aneurysm. Cephalgia. 1994;14(2):79-87.
8. van Gijn J. Subarachnoid haemorrhage. Lancet. 1992;339(8794):653-655.
9. Boesiger BM, Shiber JR. Subarachnoid hemorrhage diagnosis by computed tomography and lumbar puncture: are fifth generation CT scanners better at identifying
subarachnoid hemorrhage? J Emerg Med. 2005;29(1):23-27.
10. van der Wee N, Rinkel GJ, Hasan D, van Gijn J. Detection of subarachnoid haemorrhage on early CT: is lumbar puncture still needed after a negative scan? J Neurol
Neurosurg Psychiatry. 1995;58(3):357-359.
11. O´Neill J, McLaggan S, Gibson R. Acute headache and subarachnoid haemorrhage: a retrospective review of CT and lumbar puncture findings. Scott Med J.
2005;50(4):151-153.
12. Sidman R, Connolly E, Lemke T. Subarachnoid hemorrhage diagnosis: lumbar
puncture is still needed when the computed tomography scan is normal. Acad
Emerg Med. 1996;3(9):827-831.
13. Sames TA, Storrow AB, Finkelstein JA, Magoon MR. Sensitivity of new-generation
computed tomography in subarachnoid hemorrhage. Acad Emerg Med. 1996;3(1):1620.
14. Dieterich M, Perkin GD. Post lumbar puncture headache syndrome. In: Brandt
J, Caplan LR, Dichland J, Diener HC, Kennard C, eds. Neurologic Disorders: Course
and Treatment. San Diego, CA: Academic Press; 1996:59-63.
15. Beijnum J, Straver DC, Rinkel GJ, Klijn CJ. Spinal arteriovenous shunts presenting as intracranial subarachnoid haemorrhage. J Neurol. 2007;254(8):1044-1051.
16. Vermeulen M, Hasan D, Blijenberg BG, Hijdra A, van Gijn J. Xantochromia after
subarachnoid haemorrhage needs no revisitation. J Neurol Neurosurg Psychiatry.
1989;52(7):826-828.
www.neurosurgery-online.com
CT SCANNING IN SAH EARLY DETECTION
COMMENTS
C
ortnum et al present a large retrospective study aimed at evaluating
the sensitivity and specificity of modern computed tomography (CT)
scanners in accurately diagnosing subarachnoid hemorrhage (SAH), and
they re-evaluate the conventional wisdom and previous recommendation to perform lumbar puncture in cases of suspected SAH and a negative CT scan.
This group retrospectively analyzed 499 patients presented to their hospital over a period of 5 years and found only a single case (in which the patient
presented on day 6) of positive lumbar puncture and negative CT scan. The
CT scanning sensitivity was thus 99.7% and the specificity was 100%.
The authors concluded that CT scan is sufficient to diagnose SAH in the
first 3 days of presentation and it seems to be safe to leave out lumbar
puncture from day 1 to day 3 if the CT scan is negative.
We like this manuscript. The methodology is sound, and the hypothesis addresses an important clinical question. Whereas the real risk of
lumbar puncture is small, too often the analysis of a negative CT scan is
confounded by spurious data obtained by a traumatic lumbar puncture
performed by an inexperienced non-neurosurgeon. This sort of data
invariably confounds and complicates the assessment of the case and confuses the patient and family. It seems reasonable to adopt a CT-only policy for the first 3 days following “ictus.” Whether practitioners will actually
modify their algorithms is a different matter.
Zakaria Hakma
Christopher M. Loftus
Philadelphia, Pennsylvania
F
rom a major neurosurgical center in Denmark, the authors report the
reliability of CT scanning in the early detection of SAH. Using lumbar puncture as the reference standard, they confirm their hypothesis that
modern (fifth generation) CT scanners offer excellent sensitivity and specificity compared with earlier models. They suggest that lumbar puncture
is not necessary to exclude SAH in the first 3 days after ictus if the CT
scan is negative.
The study consisted of nearly 500 patients who were thought to have
SAH. Approximately 200 of the patients had negative CT scans and
underwent lumbar puncture. In all of these patients but one, the lumbar puncture was “negative.” The last patient, who presented on postbleed day 6, had a negative head CT but “positive” lumbar puncture.
The remaining 300 patients had positive CT scans. From these data, the
authors calculate that CT scanning has a sensitivity of 99.7% and a specificity of 100%, although the latter parameter is essentially tautologous.
The authors do not specify the basis of reporting a “negative” vs “positive” lumbar puncture result, nor do they indicate how they distinguished
a traumatic lumbar puncture from true subarachnoid hemorrhage. Presumably, these designations are based on the presence or absence of xanthochromia. However, there may be institutional variability in the way by
which xanthochromia is measured. Rather than using quantitative spectrophotometry, some laboratories merely perform visual inspection of
the supernatant. Furthermore, as the authors note, xanthochromia takes
several hours to appear, so a lumbar puncture performed shortly after
the onset of SAH may yield false negative results. Similarly, xanthochromia may disappear at varying rates, and the absence of xanthochromia
days after an event can not reliably exclude prior SAH. Also, xanthochromia on lumbar puncture may be the only means of detecting a “sentinel”
hemorrhage in the setting of a negative CT. Finally, CT scan interpretation is inescapably subjective. The authors caution that the CT images
should always be evaluated by either a neurosurgeon or a dedicated neuroradiologist if the diagnosis of SAH is to be excluded without doing a
lumbar puncture.
Despite these limitations, this study provides important data about
the reliability of modern CT scanners and is likely to change clinical
practice.
Arun Paul Amar
Los Angeles, California
FUTURE MEETINGS—CONGRESS OF NEUROLOGICAL SURGEONS
The following are the planned sites and dates for future annual meetings of the Congress of Neurological Surgeons:
NEUROSURGERY
2010
San Francisco, CA
October 23–28
2011
Washington, DC
October 1–6
2012
Chicago, IL
September 29–October 4
2013
San Francisco, CA
October 19–24
VOLUME 66 | NUMBER 5 | MAY 2010 | 903
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