SWI is a superb protocol of increasing use, now being included in MRI protocols of a number of neurological diseases because of its high sensitivity. Any tissue that has a different susceptibility than its surrounding structures such as deoxygenated blood, hemosiderin, ferritin and calcium can be easily detected by SWI [14].
SWI was previously known as blood oxygen level-dependent imaging (BOLD) as it provides us with information on the blood oxygen level in vessels especially the venous drainage and its signal intensity. The uncoupling of oxygen supply and demand in hypoperfused brain tissue may result in a relative rise of deoxyhemoglobin levels and a decrease of oxyhemoglobin levels in tissue capillaries and draining veins, which accounts for the greater visibility of veins in this region [5]. SWI allows early detection of hemorrhage, identifies microbleeds and can detect an intravascular clot in the acute stage. It has also been found to provide information on tissue viability focusing on the signal intensity within the draining veins to evaluate ischemic penumbra [7].
In the current study, SWI revealed one case with a hypointense signal and slightly prominent veins draining the infarct area and extending beyond the infarct, suggestive of penumbra. Sorimachi et al. [15] demonstrated that dilated cortical veins detected on SWI may represent regions with higher oxygen extraction fractions due to chronic ischemia.
Four cases of moyamoya disease were demonstrated on SWI, of which one showed an added hemorrhagic component. According to Horie et al. [16], SWI can be used to assess the severity of moyamoya disease by analyzing the number of draining intramedullary veins, giving the brush-like appearance or “brush-sign”. The number of the conspicuous deep medullary veins draining into the subependymal veins was classified: stage 1, mild (< 5); stage 2, moderate (5–10); and stage 3, severe (10) [16]. In our study, two patients were stage 2 and two were classified as stage 3.
Our study revealed nine children with cerebral venous thrombosis, 6/9 was venous sinus thrombosis which was correctly diagnosed by the SWI, while 3/9 were cortical vein thrombosis, where the SWI missed one case of them which was subtle in the SWI and interpreted as normal cortical vein (FN), yet the follow-up CT and MRI done two and 4 days later respectively proved that it was cortical vein thrombosis, in the other hand, the SWI overestimated prominent cortical veins as cortical vein thrombosis in two children (FP). SWI can detect the venous infarcts which are frequently hemorrhagic, even the small microbleeds and is a good technique to demonstrate the thrombosed veins [17]. Our study agreed with Thomas et al. [18] who found that susceptibility-weighted imaging facilitates the detection of venous sinus thrombosis otherwise difficult to detect in conventional MRI images.
An emergency cerebrovascular disease that requires urgent diagnosis to minimize potential complications is TBI. We had 10 cases of TBI, most of which were diffuse axonal injury appearing as scattered microbleeds which were inconspicuous on the T1 WI yet more evident on the SWI with an excellent demonstration by the filter phase as regards signal, size and number of microbleeds with a p-value of 0.005. Our results were similar to those of Sinha et al. [19] and Sultan et al. [20], who found that the SWI was superior to conventional MRI for microbleed detection, with p-values of 0.001 and 0.006, respectively. Hamdeh et al. [21] and Babikian et al. [22] both emphasized the sensitivity and significant role of SWI in detecting the size, distribution, and number of hemorrhagic lesions in DAI. According to Ashwal et al. [23], SWI may provide more accurate prognostic information regarding the long-term neurophysiologic outcome as regards TBI. Lawrence et al. [24] study revealed that using SWI to detect DAI microbleed gives an objective early marker of damage severity following trauma.
Acute necrotizing encephalopathy of children is a fulminant form of encephalopathy resulting in rapid and progressive symptoms of brain dysfunction [25]. The classic picture is concentric laminar lesions in both thalami [26]. However, the presence of hemorrhage is a sign of severity and its demonstration is crucial to assess the outcome. This study included only 5 patients with ANEC because it is a rare entity, of which SWI was able to show the hemorrhagic component very clearly with small petechial hemorrhages seen not only in the thalami but also in the cerebellum and brain stem. SWI was an excellent modality and was the only sequence capable of adding more detail as regards the small petechiae of hemorrhage. This is in agreement with Manara et al. [27] who emphasized that the SWI is a crucial study for demonstrating tiny petechial hemorrhage, which is frequently obscured in the conventional MRI sequences.
Five cases of cavernomas were included in our study, two presented with headache, one with seizure, one with arm numbness and one with leg weakness. All cavernomas were clearly evident and excellently demonstrated on SWI sequence especially on the filter phase, while two of them were obviously seen in the SWI and overlooked on the conventional sequences due to their small size. Sultan et al. [20] also observed a greater SWI detection rate for cavernoma, with a p-value of 0.004. Our study agreed with Sparcia et al. [28] who stated that SWI is the best MRI sequence for cavernoma detection.
The high spatial resolution of SWI and increased contrast of SWI increased the confidence of the radiologists in the diagnosis, especially for the less experienced ones. The SWI demonstrated a substantial to almost complete interobserver agreement for identification of hemorrhagic, ischemic, and the whole lesions, which was consistent with El-Serougy et al. [29] study, which revealed an almost perfect agreement for the detection of cerebral microbleed with a k value of 0.84. Potential problems connected to the use of SWI, according to Bosemani et al. [30], include pitfalls owing to variations in blood oxygenation levels, blood flow, potential pitfalls related to magnetic field intensity, pitfalls due to misinterpretation of localization on minIP images, and mimickers such as gas. It's critical to be aware of these pitfalls to avoid misinterpretation or misdiagnosis.
Limitation
Our study had limitations, the first was the relatively small number of patients. Our results were also obtained on a 1.5 T MRI which may not directly translate to imaging at 3 T, as the field strength is known to affect sensitivity for detection of hemorrhage and vessels. Lastly, we recommend the use of quantitative susceptibility mapping; a novel sequence under several trials in the staging of hemorrhage and in observing iron content changes over time.