**4. Diagnosis of cAVMs**

Diagnosis of cAVMs must include a detailed assessment of the nidus and the adjacent structures. Plain CT is the initial diagnostic tool for cAVM patients who present with one of previously mentioned clinical manifestations, while CT angiography or digital subtraction angiography are used to locate the exact site of rupture in patients with ICH. Magnetic resonance imaging (MRI) is the recommended investigation for patients with nonhemorrhagic manifestations. Digital subtraction angiography is the investigation of choice for the characterization of the feeding arteries, nidus angioarchitecture, and draining veins and is mandatory for precise AVM grading and management planning [2, 4].

#### **4.1 Computerized tomography (CT) and related techniques**

CT scan is the first radiological investigation that is performed in patients who present with convulsions, focal neurological deficit, or clinical signs of ICH. Plain head CT is useful for confirming ICH or assessing abnormal suspicious dilated dural veins, abnormal faint hyperdense cerebral mass, and focal cerebral calcification, which are alert signs for the radiologist for the possibility of underlying cAVMs; however, negative CT scan cannot be excluding the presence of cAVMs. Compression of the nidus by hematoma impedes CT diagnosis of cAVM in patients with acute ICH. Therefore, CT angiography should be done promptly to diagnose the underlying cAVMs. CT angiogram with intravenous iodinated contrast media with images acquired by bolus tracking technique is very helpful for maximum cerebral as well as cAVM arterial opacification. The CT head angiogram is used for confirming the diagnosis, assessing the cAVM size, site, number, and origin of feeding arteries and draining vein as well as the presence of associated aneurysm and site of bleeding. The high spatial resolution of CTA allows the generation of multiplanar reformations, maximum intensity projections, and volumetric reconstructions for analysis (**Figures 3**–**5**) [4, 16, 18].

*Cerebral Arteriovenous Malformations (cAVMs): What Is New? DOI: http://dx.doi.org/10.5772/intechopen.90096*

#### **Figure 3.**

*Plain CT head (A) and CT head angiogram (B) of young adult patient demonstrate right parietal parenchyma brain hemorrhage (the arrow on A image) and multiple serpiginous tortuous vascular malformation AVM (the arrow on the B image) [15].*

#### **Figure 4.**

*Plain CT shows hyperdense tortuous structure at lateral ventricular region representing AVM [16].*

#### **Figure 5.**

*CT head angiogram MIP (maximum intensity projection) axial and sagittal view (A and B respectively) demonstrates right occipital lobe AVM supplied mainly by right posterior cerebral artery and drained to straight and right transverse dural sinuses [17].*

In recent decades, the radiological equipment has showed visible development making us more aware of the pathophysiology of many diseases by using perfusion CT and MRI scan for cAVMs to provide information regarding the blood flow abnormality within and around such vascular anomalies by assessing cerebral blood flow (CBF), cerebral blood volume (CBV), and the mean transient time (MTT). Through these, we can demonstrate three different forms of extra-nidal parenchymal perfusion abnormalities:

1.Functional steal is characterized by redistribution of the blood flow from surrounding brain tissue through the arteriovenous malformation that leads to disturbance of normal cerebral perfusion. Patients with this phenomenon usually present with convulsions. CT scan shows decrease in CBV, CBF, and MTT as a result of sump effect from the artery supplying the arteriovenous malformation **Figures 6** and **7**.

#### **Figure 6.**

*Normal and Perfusion abnormalities diagram in cAVMs. (A) Illustrate normal brain tissue blood flow. (B) Illustrate the abnormal brain tissue blood flow within and adjacent to the AVM. The Black arrow represent functional steal region in which the blood shunted away to the nearby AVM. The red arrow representing ischemic steal region due to indirect collateral of the near the AVMs. The blue arrow is a brain region drained by high pressure veins of AVM leading to venous congestion [15].*

#### **Figure 7.**

*Illustrate the effect of steal phenomenon in Brain's AVM on adjacent brain tissue (A) and (B) CT angiograms demonstrate right side occipital AVM (arrows). Selected images from brain CT perfusion (C and D) shows high CBF (black arrows in C) and CBV (black arrows in D) in the nidus and low CBF (white arrows in C) and CBV (white arrows in D) in the perinidal area, suggestive of perinidal ischemia. There is no evidence of cerebellar ischemia on the FLAIR (E) and diffusion (F) images. CBF (arrows in G) and CBV (arrows in H) are low in the contralateral cerebellar hemisphere, suggestive of cerebellar diaschisis [19].*

*Cerebral Arteriovenous Malformations (cAVMs): What Is New? DOI: http://dx.doi.org/10.5772/intechopen.90096*


### **4.2 Magnetic resonance imaging (MRI) of the brain and related techniques**

MRI of the brain is very sensitive for the exact determination of the cAVM nidus location and an associated draining vein; it also has exclusive sensitivity in determining remote bleeding due to these lesions. On noncontrast brain MRI, the cAVM nidus is seen as signal void on T2-weighted images with dilated feeding arteries and draining veins, and susceptibility-weighted imaging can detect the presence of hemosiderin component of chronic bleeding as low signal intensity. The ischemic and brain steal area can appear as hyperintense T2 weighted and FLAIR. MRA also could be used to add crucial information regarding the feeding arteries, draining veins, and the presence of associated aneurysm, which appear Could be gained from CT perfusion (CTP). The same pathophysiological information that could be gained from CTP can also be done by MRI perfusion using noncontrast ALS (arterial spine labeling) technique or with the usage of contrast media **Figures 8** and **9** [2, 4].

MRI of the brain is especially valuable in follow-up patients after treatment. After radiosurgery, MRI is essential to follow up regression of the nidal volume. While the MR angiography is very useful to characterize the venous drainage and other vascular features, the adjacent tissue that is exposed to the radiation field can be precisely observed for posttherapy edema or radiation necrosis [4, 16].

#### **4.3 Digital subtraction angiography (DSA)**

Digital subtraction angiography is the gold standard for assessment of nature and number of the feeding arteries, presence of flow-related aneurysms, quality of venous drainage, associated varices, and stenosis.

#### **Figure 8.**

*MRI brain of an adult patient T2-weighted image A and SWI (susceptibility weighted image). B demonstrates right temporal T2WI and DWI serpiginous hypointensity representing AVM [20].*

#### **Figure 9.**

*MRI T2-weighted image A&B and MRA brain C&D images the brain demonstrate T2 weighted signal void serpiginous structure at left inferior parietal lobe; on MRA, images show the nidus fed by arterial feeder from left middle cerebral artery and drained to superficial cortical veins to left transverse sinus [16].*

Two types of feeding arteries that can be identified by DSA are as follows:


Flow-related aneurysms in the feeding arteries usually result from amplified shear stress and considered as an indicator of vascular friability and hemorrhage risk. These aneurysms may resolve following curative treatment of the AVM. Intranidal aneurysms are usually small, less than 3 mm, and pseudoaneurysms and can be successfully treated with embolisation.

The AVM nidus may have both fistulous and glomerular compartments; the fistulous compartments form high-flow shunt that can be treated with endovascular therapy, while the glomerular compartments form an intervening network of pathological vessels and are very difficult to treat with embolisation.

Assessment of the venous part of AVM is critical and should include the anatomy of drainage (superficial, deep, or mixed) and characteristics of the venous outflow (focal stenosis, venous pouches, and sinus stenosis or occlusion). Drainage into the deep venous system is associated with a high risk of bleeding and indicates deep location that may make surgical intervention difficult [2, 4].
