Localized pseudo-subarachnoid hemorrhage

Abstract

Background: To analyze the imaging and clinical data of patients with localized pseudo-subarachnoid hemorrhage (pseudo-SAH), so as to improve the correct understanding of this sign by radiologists. 

Methods: The imaging and clinical data of patients with localized pseudo-SAH on head CT scan without contrast from January 2013 to March 2022 were retrospectively analyzed, and the imaging and clinical characteristics were summarized. 

Results: The etiology of 9 patients with pseudo-SAH was viral encephalitis (2 cases), acute cerebral infarction (4 cases) and hypoxic ischemic encephalopathy (3 cases). All patients underwent CT scan without contrast, CT scan with contrast, MRI and lumbar puncture examination. All patients' head CT scan without contrast showed local swelling of brain tissue (less than two lobes), stenosis and occlusion of adjacent subarachnoid space, with its inner strip of high-density shadow. CT scan with contrast found that the high density shadow was significantly enhanced. MRI and lumbar puncture were performed to rule out true SAH and confirm pseudo-SAH. Finally, 8 patients were discharged from hospital after treatment, and 1 patient died of multiple organ failure. 

Conclusion: Localized pseudo-SAH often indicates localized brain lesions and has a relatively good prognosis. It has certain characteristics in CT value, enhancement mode and morphology.

Background

Acute subarachnoid hemorrhage (SAH) is common in emergency head Computed tomography (CT), often presenting as a linear dense shadow in the subarachnoid space. CT, as the first choice for the diagnosis of SAH, has been recognized for its sensitivity and specificity. However, there are some false positive diagnoses in practical work, which brings a series of potential problems, including wrong treatment and unnecessary examination. The CT findings are identical to those of true acute SAH, but there is no blood in the subarachnoid space. We refer to this sign as pseudo-subarachnoid hemorrhage (pseudo-SAH). Previous reports have suggested that pseudo-SAH is mainly caused by extensive strips of high-density shadows in basal cisternae, lateral fissure cisternae, and subarachnoid space on the basis of widespread diffuse cerebral edema or after intravenous injection of contrast agent^[1–3]. There is little knowledge and literature about this sign, especially in the local sulci (less than two lobes) and cisternae. In order to improve the understanding of this sign and reduce misdiagnosis, this paper collected the imaging and clinical data of patients with localized pseudo-SAH, analyzed its CT manifestations, occurrence mechanism and clinical significance, and conducted a literature review.

Methods

Study subjects 

From January 2013 to March 2022, a total of 9 cases with localized pseudo-SAH on CT scan without contrast were collected. Patients were included with other tests (CT scan with contrast, MRI, and lumbar puncture) to exclude true SAH.

Examination and scanning parameters

All patients included CT scan with/without contrast, MRI and lumbar puncture. GE Discovery CT750 HD spectral CT and GE Discovery MR750 3.0T superconducting imager were used. CT scanning parameters: scanning mode spiral scanning, tube voltage 120kv, tube current 200mA, pitch 1.375:1, layer thickness 5.0mm, image matrix 512 × 512, field of view (FOV) 360mm, thin reconstruction layer thickness 1.25mm. Contrast agent iohexol (50 ml:15 g (I)) was injected through elbow vein with high-pressure syringe for scanning with contrast. The dose was 80-100 ml, and the injection flow rate was 2.5-3.0 ml/s, two-phase enhanced scanning was performed 60-90 s after injection. MRI uses 32 channel high-resolution head coil to collect T1WI, T2WI, T2 Flair, DWI, MRA and SWI.

Evaluation criteria

The image data of all patients were observed, diagnosed and analyzed by two senior imaging diagnostic doctors to reach a consensus diagnosis.

Results

Basic information

A total of 9 patients with pseudo-SAH were enrolled. All patients were admitted to the hospital in emergency. Among the 9 patients, 3 had headache with hemiplegia, 2 had dizziness, 2 had headache with slurred speech, and 1 had headache with nausea and 1 had epilepsy. Two patients were finally diagnosed with viral encephalitis, four with acute cerebral infarction, and three with hypoxic ischemic encephalopathy. After treatment, 8 cases improved and discharged, and 1 case developed multiple organ failure and died. Table 1.

Imaging examination and related auxiliary examination

CT scan without contrast of the head showed reduced density of localized brain tissue (less than two lobes), stenosis and occlusion of the adjacent subarachnoid space, with dense internal strip (Figure 1). Contrast-enhanced CT showed significant enhancement of the above high density strip in the subarachnoid space (Figure 2). MRI: the brain tissue in the corresponding region was obviously swollen, with T1WI hypointensity and T2WI hyperintensity. Flair and DWI showed hyperintensity, but no obvious abnormal signal shadow was found in the cists adjacent to the sulci (Figure 3). MRA revealed a mild local stenosis of the M2 segment of the right middle cerebral artery. SWI sequence scan did not find obvious bleeding signs. A lumbar puncture also did not reveal bloody cerebrospinal fluid.

Discussion

Pseudo-SAH was first discovered by Spiegel et al., that linear high-density shadows similar to SAH appeared in sulci, cisternae and subarachnoid space on head CT of patients with cerebral edema^[4]. However, Avrahami et al. confirmed by lumbar puncture or autopsy that there was no real SAH in these patients and called it pseudo-SAH^[5]. The pseudo-SAH reported in the previous literature is based on a large range of diffuse brain edema, and the basal cists, sulci, and fuses in the pseudo-SAH are often similar to SAH. The underlying diseases of these patients are mostly ischemic hypoxic encephalopathy, massive cerebral infarction, venous sinus thrombosis, severe craniocerebral injury, spontaneous intracranial hypotension, acute purulent meningitis, intrathecal or intravascular contrast agent injection, etc^[1-5]. The etiologies of the patients with localized pseudo-SAH in this study were ischemic hypoxic encephalopathy, acute cerebral infarction, and viral encephalitis. The basic disease spectrum of pseudo-SAH in this study was basically the same as that reported in previous literature. It has even been reported that the occurrence of pseudo-SAH may be one of the early CT manifestations of acute cerebral infarction^[6].

On the basis of localized cerebral parenchyma edema, linear relatively high density shadows appeared in the adjacent sulci and cisternae of all patients, and even the linear high density shadows were significantly enhanced in the contrast-enhanced CT, suggesting that the linear high density shadows may be some vascular structures with relatively high density. As for the mechanism of this illusion, we speculate that this illusion may be caused by the compression of venous sinuses by localized cerebral edema, resulting in blocked venous return and dilation of superficial veins, which is in contrast to the brain parenchyma with reduced density, resulting in an illusion similar to SAH. Or due to the acute cerebral vascular occlusion of the distal side of the affected side, the local leptomeningeal collateral blood flow slowly formed relatively high density shadow of the lumen^[6]. Or local lesions may lead to the destruction of the blood-brain barrier and increase the permeability of the meninges, thereby causing the density of the subarachnoid space to increase^[7].

Although there are many similarities between localized pseudo-SAH and real SAH CT manifestations, there are some differences between them: ①Density: Most previous studies distinguish real SAH from pseudo-SAH by comparing CT values, and it has certain clinical significance. The relative high density shadow density in pseudo-SAH is lower than that in real bleeding, CT values are 29-33 Hu^[8], and 60-70 Hu^[9], respectively. ②Enhancement method: high-density images of pseudo-SAH can significantly enhance in contrast-enhanced CT, which is significantly different from SAH^[5]. ③Morphology: Patients with pseudo-SAH have relatively narrow or occluded subarachnoid spaces such as adjacent sulci and cisterns due to the cause of cerebral edema, whereas patients with SAH show enlarged subarachnoid spaces such as cisterns at an early stage due to poor cerebrospinal fluid circulation caused by the blockage of hematoma.

The pathologic changes of SAH patients will gradually absorb and decrease over time, and generally disappear completely within 3 weeks, while those of pseudo-SAH are mainly related to the primary underlying disease and its treatment situation, and some patients can even persist^{[10, 11]}. Regarding the prognosis of pseudo-SAH, previous studies have shown that the prognosis is mainly related to the underlying diseases of patients. Some studies also believe that the occurrence of pseudo-SAH means that patients have severe brain edema and poor prognosis^{[8, 12]}. In contrast, all cases of localized pseudo-SAH arose on the basis of localized cerebral edema, generally suggesting localized brain tissue lesions with limited lesion extent, lesser extent, and mostly better prognosis. MRA in the present study revealed one case with localized mild stenosis in the M2 segment of the right middle cerebral artery, which was relatively mild in extent and extent in this patient, which was also consistent with the limited extent of the lesion. After aggressive treatment of the primary underlying disease, 8 of the 9 patients in this paper improved, and only 1 patient died from conversion to multiple organ failure, suggesting that the prognosis of small-scale pseudo-SAH is relatively good.

Conclusions

There are some similarities between pseudo-SAH on CT findings and real SAH. Usually the presence of local pseudo-SAH indicates localized brain edema, suggesting better prognosis sage, which has certain characteristics in density, enhancement modality, morphology, correct recognition of imaging features, combined with clinical data, can improve the accuracy of its imaging diagnosis and avoid unnecessary treatment.

Abbreviations

Subarachnoid hemorrhage: SAH

Computed tomography: CT

Pseudo-subarachnoid hemorrhage: pseudo-SAH

Field of view: FOV

Declarations

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Acknowledgements

The authors would like to thank all participants for their time and effort.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.”

Author information

Authors and Affiliations

Department of Radiology, Hospital of Chengdu University of Traditional Chinese Medicine, Chengdu, 610075, SiChuan, People’s Republic of China

Hui Sun, Sha Jian, Jing Dai, Jian Hou, Bo Peng

Clinical Medicine, Chengdu University of Traditional Chinese Medicine Shierqiao Campus, Chengdu, 610072, SiChuan, People’s Republic of China

Hui Sun, Jingwei Li

Contributions

HS, SJ and BP contributed to the conception and design of the study, Conceptualization, Methodology, and Data curation. YLY wrote the manuscript. JH supervised the research. JD and JWL collected the data. All authors read and approved the final manuscript.

Ethics declarations

Ethics approval and consent to participate

This study was approved by the Hospital of Chengdu University of Traditional Chinese Medicine Research Ethics Committee, and the Hospital of Chengdu University of Traditional Chinese Medicine Research Ethics Committee waived the need for patient informed consent. We confirmed that all methods were performed in accordance with the relevant guidelines and regulations (For example: Declarations of Helsinki).

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

References

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Table

Table 1 clinical data of patients with localized pseudo-SAH