Abstract
Pseudo-subarachnoid hemorrhage (pseudo-SAH) is a radiologic
phenomenon where imaging characteristics mimic those of true
subarachnoid hemorrhage (SAH), despite the absence of actual
hemorrhage. This paper aims to elucidate the underlying
mechanisms, diagnostic challenges, and clinical implications
of pseudo-SAH, with a particular focus on differentiating it
from true SAH using imaging modalities and clinical context.
Introduction
Subarachnoid hemorrhage (SAH) is a critical condition with
high morbidity and mortality, necessitating prompt and
accurate diagnosis. However, certain conditions can mimic the
appearance of SAH on imaging studies, leading to potential
misdiagnosis and inappropriate management. Pseudo-SAH is one
such phenomenon, often seen in patients with diffuse cerebral
edema, intracranial hypotension, or following cardiopulmonary
arrest. This paper reviews the etiology, diagnostic criteria,
and implications of pseudo-SAH, highlighting the importance of
accurate differentiation from true SAH [1,2].
Etiology and Pathophysiology
Pseudo-SAH can arise from various conditions, including:
Diffuse Cerebral Edema: Severe brain swelling can
increase the attenuation of the cerebrospinal fluid (CSF)
spaces on CT, mimicking SAH [3].
Intracranial Hypotension: Reduction in CSF volume can
lead to dural venous sinus engorgement and increased
attenuation of the basal cisterns.
Post-Cardiac Arrest: Global cerebral ischemia following
cardiac arrest can cause brain swelling and increased
attenuation of the CSF spaces.
Meningitis and Encephalitis: Severe infections can lead
to brain swelling and increased protein content in the CSF,
leading to higher attenuation on imaging.
Diagnostic Imaging
Computed Tomography (CT)
CT imaging is the first-line modality for diagnosing SAH. In
pseudo-SAH, the increased attenuation in the basal cisterns
and cortical sulci can mimic true hemorrhage. Key features
include [4]:
Basal Cisterns and Cortical Sulci: Hyperattenuation in
these areas without the presence of true blood.
Brain Parenchyma: Diffuse cerebral edema may be
present, with loss of gray-white matter differentiation.
Magnetic Resonance Imaging (MRI)
MRI can provide additional clues to differentiate pseudo-SAH
from true SAH:
FLAIR Sequence: May show hyperintense signal in the
basal cisterns due to edema rather than blood.
Diffusion-Weighted Imaging (DWI): Can reveal areas of
restricted diffusion indicative of cytotoxic edema.
Susceptibility-Weighted Imaging (SWI): Helps in
identifying true blood products through susceptibility
effects, which are absent in pseudo-SAH.
Angiography
Digital subtraction angiography (DSA) may be performed to rule
out vascular causes of true SAH, such as aneurysms or
arteriovenous malformations. In pseudo-SAH, DSA typically
shows no vascular abnormalities.
Clinical Presentation
The clinical presentation of patients with pseudo-SAH varies
based on the underlying cause:
Diffuse Cerebral Edema: Patients may present with
altered mental status, coma, or signs of increased
intracranial pressure [5].
Intracranial Hypotension: Symptoms include orthostatic
headaches, nausea, and vomiting.
Post-Cardiac Arrest: Patients typically present with
global hypoxic-ischemic encephalopathy and coma.
Meningitis/Encephalitis: Symptoms include fever,
headache, neck stiffness, and altered mental status.
Management
The management of pseudo-SAH focuses on addressing the
underlying cause:
Cerebral Edema: Osmotherapy, hyperventilation, and
surgical decompression may be considered.
Intracranial Hypotension: Epidural blood patch and bed
rest are common treatments.
Infectious Causes: Appropriate antibiotic or antiviral
therapy is essential.
Post-Cardiac Arrest: Neuroprotective measures and
supportive care are crucial.
Conclusion
Pseudo-SAH represents a diagnostic challenge due to its
imaging resemblance to true SAH. Accurate differentiation is
essential to avoid unnecessary interventions and to guide
appropriate management. Advanced imaging techniques and
careful clinical correlation are pivotal in distinguishing
pseudo-SAH from true hemorrhage. Understanding the underlying
etiologies and pathophysiology can aid clinicians in making
informed decisions and improving patient outcomes.
References
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2. Heck DV, et al. Pseudo-subarachnoid hemorrhage: a potential
imaging pitfall. Emerg Radiol. 2009;16(3):205-209.
3. Chan SS, et al. Differentiating true subarachnoid
hemorrhage from pseudo-subarachnoid hemorrhage in patients
with diffuse brain edema: a retrospective cohort study. BMC
Neurology. 2019;19(1):77.
4. Bradley WG, et al. Pseudo-subarachnoid hemorrhage:
computed tomographic appearance in cases of severe cerebral
edema. Radiology. 1993;186(2):319-322.
5. Zouaoui B, et al. Pseudo-subarachnoid hemorrhage: a
comparative study of CT findings and their clinical relevance.
Neuroradiology. 2008;50(7):607-614.