rete mirabile ( rm ) is an arterial or arteriolar meshwork formed by branches from one or more arteries that converge into a single artery . carotid rete mirabile ( crm ) is a physiological network between the external and internal carotid systems that are usually located around the cavernous sinus in lower mammals , such as goats , sheep , and pigs ( 1 ) . crm is a very rare pathological condition in humans and is associated with aplasia or hypoplasia of the internal carotid artery ( ica ) , and carotid and vertebrobasilar rm ( cvbrm ) is even rarer . to the best of our knowledge , only nine cases , including six of vertebral rete ( vr ) and three of basilar rete ( br ) , have been reported . some of the patients with cvbrm presented with subarachnoid hemorrhage ( sah ) , intracerebral hemorrhage , or ischemia , but others were asymptomatic . when asymptomatic , the conditions were detected only incidentally on computed tomography ( ct ) or magnetic resonance image ( mri ) of the brain . we report the case of a patient with carotid and vertebral rm ( cvrm ) that was initially detected on mri of the cervical spine . a 28-year - old man presented with non - specific posterior neck pain radiating to the shoulder and arm , but not accompanied by sensory or motor changes . the patient was previously healthy with an unremarkable past medical history and no history of trauma . non - contrast cervical mri demonstrated tortuous vascular signal voids limited to the anterior cerebrospinal fluid ( csf ) space on t2-weighted images ( fig . the ct angiography ( cta ) performed to evaluate for abnormal vasculature showed a dilated and tortuous anterior spinal artery , focal interruption , and fusiform dilatation at the v4 segment of the vertebral artery ( fig . cta demonstrated hypoplastic cervical ica on the right side and relatively normal cervical ica on the left side . a catheter angiography was performed to investigate a spinal arteriovenous fistula ( avf ) or arteriovenous malformation ( avm ) . angiography of the right common carotid artery ( rcca ) demonstrated long segmental narrowing of the right ica ( rica ) from the proximal cervical portion and occlusion at the cavernous segment with trans - dural rete formation through the external carotid artery ( eca ) branches ( fig . selective angiography of the rica was not attempted due to narrowing of the proximal ica . angiography of the left ica ( lica ) demonstrated segmental absence of the cavernous ica with surrounding rete formation , while all segments of the lica except for the cavernous portion , middle cerebral artery ( mca ) , and anterior cerebral artery ( aca ) showed normal features . the distal basilar and posterior cerebral arteries are being filled by the posterior communicating artery and the persistent trigeminal artery ( fig . 1f ) . a left eca angiography demonstrated transdural rete formation between the internal maxillary artery and the enlarged ophthalmic artery ( fig angiography showed segmental absence at the v3 segment of the rva with surrounding tortuous dilated rete formation . a saccular aneurysm at the distal portion of the rete and fusiform dilatation of the v4 segment of the rva was demonstrated . the distal rica and right mca supplied by the posterior communicating artery ( p - com ) on rva angiography had a normal configuration ( fig . the radiculomedullary artery ( rma ) originating at the proximal rva ( at the level of the seventh cervical vertebra ) was enlarged and connected via a prominent anterior spinal artery ( fig . a left vertebral artery ( lva ) angiography revealed similar findings to those of the rva angiography , with less prominent rete formation at the v3 segment level and rma origination at the proximal lva ( at the level of the fifth cervical vertebra ) ( fig . bypass surgery was not attempted because symptoms were mild and the brain perfusion status was relatively normal . agenesis is defined as the complete failure of development of an organ ; aplasia , lack of development ; and hypoplasia , incomplete development ( 2 ) . segments of the fully developed ica correspond to embryonic structures . in segmental agenesis of the ica , each of these embryonic arteries is a potential source of reconstitution of distal flow in the ica ( 3 ) . in the pathogenesis of crm formation , the most accepted theory is the late ( fetal or perinatal ) regression of the artery ( 2 , 3 ) . mahadevan et al . ( 3 ) postulated that if agenesis is the primary deficit , the embryonic vessels should be the primary source of recruitment for collateral circulation . if the absence of the ica occur by regression after its development , the embryonic vessels are already regressed and no longer available for collateral circulation . as the crm is not present in any human developmental state ( 3 - 6 ) , it is probably a secondary change to ica regression in early development ( 6 ) . evaluation of the skull base for presence or absence of the carotid canal is required for distinguishing aplasia from agenesis , since the presence of the ica precursor is a prerequisite for the development of the carotid canal at 5 - 6 weeks of gestation . demonstration of a small carotid canal by ct is helpful for excluding acquired etiologies ; the thin and hypoplastic carotid canal demonstrated on ct supports this theory ( 6 ) . in our case , both carotid canals were demonstrated on ct even though it was very small on the right side and relatively normal on the left side . this ct finding supports the theory that the pathogenesis of crm is not agenesis , but the later regression of the artery . in this case , we could rule out the pseudorete by acquired atherosclerotic occlusion for several reasons ; 1 ) the level of segmental agenesis is bilaterally symmetrical ; 2 ) all cervical and cerebral arteries except hypoplastic right cervical ica showed normal features without stenosis or luminal irregularity ; 3 ) the patient was very young and had no risk factors for atherosclerosis such as diabetes mellitus , hypertension , hyperlipidemia , and smoking . type f refers to collateral flow to the distal ica via transcranial anastomoses from the maxillary branches of the eca as well as tiny ica collaterals , which are called rete mirabile ( in latin , " wonderful net " ) . carotid rete mirabile has the following characteristic features on angiogram : ( i ) hypoplastic ica , ( ii ) arterial plexus between the maxillary artery and cavernous portion of the ica , ( iii ) dilated ophthalmic artery , ( iv ) supraclinoid ica that is not hypoplastic and is fed by the arterial plexus and ophthalmic artery , ( v ) bilateral lesions , and ( vi ) no abnormal vessels such as moyamoya in the intradural circulation ( 2 , 7 ) . in our case , all of these features were identified on angiography . agenesis of the vertebral artery with associated rete compensation is even rarer than ica agenesis . most vrm occurs at the transdural segment with collateral circulation from the muscular and meningeal branches . to our knowledge , there are nine cases in the literature of carotid and vertebrobasilar rete mirabile in the literature ( table 1 ) . transdural rete formation was associated with vertebral agenesis in six cases ( 3 , 4 , 7 - 10 ) , while intradural rete formation associated with basilar agenesis occurred in two cases ( 2 , 6 ) , and vertebrobasilar agenesis occurred in one ( 5 ) . in only two of these cases , angiography demonstrated both transdural anastomosis via dilated anterior spinal or medullary arteries and intradural rete formation ( 3 , 7 ) . in our case , mri of the cervical spine was performed as an initial examination , and we suspected spinal dural avf . however , unlike typical avf , mri showed multiple vascular signal voids in only the anterior aspect of the spinal cord , and the dilated vessels were larger in our case than in spinal avf . crm can appear as moyamoya disease on brain mri because it demonstrates dot - like signal voids at the basal cistern ; however , the important difference between crm and moyamoya disease is that mri reveals normal supraclinoid ica , mca , and aca signal voids in crm . some mammals , such as cats , sheep , goats , oxen , and pigs , have well - developed crm as a part of their normal physiology ( to prevent overheating of the brain and regulate the pressure and flow of the cerebral blood circulation ) . in humans , however , cvbrm can be a clinically significant condition because it frequently presents with hemorrhagic and ischemic manifestations at a relatively young age . according to li et al . ( 7 ) , 27 patients with crm had variable presentations : 12 with ischemic stroke , 11 with sah , and four with intracerebral hemorrhage ( ich ) . of the nine patients with cvbrm , three presented with ischemic events including ischemic stroke in two ( a 40-year - old man and 34-year - old woman ) and temporary blindness in one ( a 29-year - old woman ) . in addition , one patient presented with carotid - cavernous fistula ( a 20-year - old man ) , one patient presented with subarachnoid hemorrhage ( a 37-year - old woman ) , and one patient presented with intracerebral hemorrhage ( a 57-year - old woman ) . the remaining three patients were asymptomatic , and cvbrm was incidentally detected in a brain ct performed after a traffic accident , or in an angiography performed for tumor embolization , or during diagnosis of avm . our patient presented with nonspecific posterior neck pain with no accompanying neurological symptoms or signs . his neck pain may bear no relation with cvbrm . associated lesions in patients with crm include intracranial aneurysm , avm , carotid - cavernous fistula , dieulafoy 's ulcer , pseudoxanthoma elasticum , and posterior fossa malformations , hemangiomas , arterial anomalies , coarctation of the aorta , and cardiac defects and eye abnormalities ( phace ) syndrome . however , only two patients with cvbrm had associated lesions including avm and pseudoxanthoma elasticum ( 8 , 9 ) . to the best of our knowledge , this is the first case where an aneurysm was demonstrated on angiography even though some cases presenting with sah or ich have been reported . rupture of an aneurysm or anastomosing vessel and hemodynamic stress may cause sah ; however , endovascular or surgical treatment is almost impossible because of tortuous and fragile collateral vessels ( 2 ) . we must recognize that cvbrm , although rare , is an important cause of strokes in young adults . an ischemic or hemorrhagic stroke is a major presentation , and can be accompanied by non - specific symptoms such as dizziness or blindness . we could also incidentally encounter this condition on mri - mra or ct - cta performed for another reason . as a result , we need to be aware of the specific mri or ct imaging and angiographic findings for this condition .
bilateral carotid and vertebral rete mirabile ( cvrm ) is a very rare condition . 
 we report a new case of cvrm initially detected by magnetic resonance imaging ( mri ) of the cervical spine . 
 mri demonstrated tortuous vascular signal voids limited to the anterior cerebrospinal fluid space mimicking spinal dural arteriovenous fistula . 
 a diagnosis of cvrm was confirmed on the basis of angiographic findings of rete formation associated with bilateral aplasia of the cavernous internal carotid and vertebral arteries without abnormal arteriovenous connection .