pediatric aneurysms are rare with an incidence of 0.6 - -4% reported in the literature . they occur more commonly in males with a ratio of 2:1 relative to the females and more commonly in the posterior circulation than in the anterior , with large and giant aneurysms being more common than simple aneurysms . incidental pediatric aneurysms need early treatment due to increased cumulative risk of rupture . in our present report we describe a case of incidentally detected completely thrombosed basilar aneurysm in a 9-year - old boy , consequently followed up for a period of 1 year by angiography with no evidence of any recanalization . the role of serial follow - up with imaging in this subgroup of aneurysms was emphasized . a 9-year - old male child with no previous significant past medical and family history presented with acute onset of imbalance to left side . clinical examination revealed truncal and gait ataxia to the left side . ct scan brain showed the presence of a round hyper dense lesion in the prepontine cistern causing mild mass effect on the adjacent pons [ figure 1 ] . magnetic resonance imaging ( t1 weighted , t2 weighted , fluid attenuation inversion recovery ( flair ) , diffusion weighted ( dwi ) , apparent diffusion coefficient , gradient echo , and time of flight ( tof ) mr angiogram sequences ) showed well defined round heterogenous lesion in the prepontine cistern on t1- and t2-weighted sequences with no foci of diffusion restriction on dwi , with minimal mass effect . tof mr angiography showed absent flow signal in the basilar and its branches with bilateral posterior cerebral arteries being filled from the posterior communicating arteries [ figure 2 ] . these findings were suggestive of thrombosed aneurysm ; however we went ahead with digital subtraction angiogram ( dsa ) to confirm the same . there was no flow seen in the basilar on vertebral angiogram [ figure 3 ] with good reformation of the bilateral posterior cerebral arteries from the posterior communicating arteries on internal carotid angiograms . detailed screening was done to rule out any associated conditions such as autosomal dominant polycystic kidney disease ( adpkd ) , fibro muscular dysplasia , and coarctation of aorta , ehlers syndrome , and marfans syndrome . plain ct scan showing a well - defined hyperdense lesion with surrounding calcification predominantly in the prepontine cistern mri t1-weighted image ( a ) showing the hypointense well - defined lesion in the prepontine cistern which is heterogenous with minimal mass effect on t2- weighted ( b ) image . mr angiogram time of flight ( c ) showing the absent signal in the basilar with bilateral dominant posterior communicating arteries ( arrows ) ( a and b ) vertebral angiogram with absent flow in the basilar with no filling of the aneurysm in early and late phases ( c and d ) bilateral posterior cerebral arteries were reformed by the posterior communicating arteries on internal carotid angiograms the symptoms of the child improved gradually over the next 1 month . in order to detect any possible recanalization over the course of time we followed up the child with repeat angiography at an interval of 1 year . we did not find any evidence of recanalization and the angiographic findings [ figures 4 and 5 ] were same as before . ct ( a ) and mr ( b ) images repeated after one year showing the thrombosed aneurysm as depicted by the arrows ( a ) vertebral angiogram done after 1 year showed no recanalization ( b and c ) bilateral posterior cerebral arteries were reformed by the posterior communicating arteries on internal carotid angiograms on townes view pediatric aneurysms contribute 0.6 - 4% of all cerebral aneurysms with a male preponderance and commonly being in the posterior circulation . our present case is a case of basilar tip aneurysm detected due to spontaneous thrombosis causing mass effect on the brain stem , which was followed up for a period of 1 year to detect any recanalization with the aim of early treatment . the occurrence of spontaneous thrombosis in nongiant aneurysms has been rarely reported and is even more rare in the pediatric age group . various factors play an important role in the balance between thrombogenesis and thrombolysis in the lumen of the aneurysm . the event can be either asymptomatic or mimic a tumor or present with ischemic stroke . described three cases of spontaneous thrombosis of saccular aneurysms presenting with ischemic stroke . in our present case we postulate that initial presentation of the child with neurodeficit was due to the mass effect on the brain stem during the event of spontaneous thrombosis of the basilar tip aneurysm . the natural history of these spontaneously thrombosed aneurysms is not yet clearly understood , hence serial neuroimaging follow - up is suggested since the mortality rate due to the rupture varies from 32% to 50% we present a rare case of spontaneously thrombosed nongiant basilar tip aneurysm confirmed with ct , mr , and dsa . the importance of serial follow - up in these cases was emphasized . to our knowledge this is the first case report of spontaneous thrombosis of nongiant basilar aneurysm presenting as an acute event and simultaneously followed up to rule out the early recanalization and to understand the natural history .
the incidence of pediatric aneurysms is rare compared to that of the adults . 
 the natural history and the course of these aneurysms were not well understood . 
 we present a rare case of spontaneously thrombosed basillar tip nongiant aneurysm in a 9year - old male child who presented with symptoms of mass effect and subsequently followed up by imaging over a period of 1 year .