Objective To study MRI diagnosis and differential diagnosis of posterior fossa cyst with hydrocephalus in children. Methods MRI performances and clinical data of 56 children with cyst in the posterior fossa and hydrocephalus were analyzed and classified.Results 12 cases of Dandy-Walker malformation(DWM)showed absence of the vermis at different degrees and the enlarged fourth ventricle widely communicating with the large posterior fossa cyst,accompanied by elevation of the tentorium cerebella and hydrocephalus,in which 1 case combined with callosal agenesis,1 case with subependymal gray matter heterotopia and 1 case with subependymal gray matter heterotopia and small occipital encephalocele.9 cases of Blake's pouch cyst(BPC)showed mildly dilatation of the fourth ventricle,and the cyst was below the cerebellar and hydrocephalus.Neither cerebellar hypoplasia nor elevation of the tentorium cerebella was observed. The postirior wall of the cyst was observed on sagittal T 2WI in 5 cases.The choroid plexus of the fourth ventricular moving to the top wall of the cyst were seen on thin sagittal T 2WI in 1 case.35 cases of arachnoid cyst(AC)showed aggregation of cerebrospinal fluid,and the fourth ventricular and aqueductal stenosis at different degrees and hydrocephalus.Conclusion MRI has evident advantages at diagnosis and differential diagnosis of cystic malformations of the posterior fossa with hydrocephalus,especially on sagittal MRI.

Objective To observe clinical and imaging findings of Kaposiform hemangioendothelioma(KHE)involved bone.Methods Data of 10 children with KHE involved bone diagnosed by surgery or biopsy pathology who underwent X-ray and non-contrast CT examination of the lesion site were retrospectively analyzed,among them 3 received enhanced CT and 9 received non-contrast MR examination.Clinical and imaging findings were observed,and the lesions were classified into type Ⅰ(confined to only bone)and type Ⅱ(involved both bone and surrounding soft tissue)according to CT findings.Results Single bone involvement was detected in 7 cases(7/10,70.00％),while multiple bone involvements were noticed in 3 cases(3/10,30.00％).CT type Ⅰ and Ⅱ were identified each in 5 cases.The median age of onset was 88.0 months,and the median course of disease was 4.0 months in type Ⅰ,all involved single bone,and the main clinical manifestations were pain but without Kasabach-Merritt phenomenon(KMP).The median age of onset was 5.0 months and the median course of disease was 1.0 months in type Ⅱ,including 3(3/5,60.00％)cases of multiple bone involvements,with swelling and limited movement of the lesion site,and KMP was observed in 2 cases(2/5,40.00％).X-ray shown most of the lesions with uneven bone density(8/10,80.00％)or lamellar low density(1/10,10.00％),while no obvious abnormality was found in 1 case(1/10,10.00％).On non-contrast CT,all affected bones in 10 cases present as worm erosion or osteolytic bone destruction,which could be accompanied by peripheral bone hyperplasia and sclerosis(8/10,80.00％),while significantly enhancement occurred in 2 cases with type Ⅱ lesion(2/3)on enhanced CT,while no obvious enhancement was found in 1 case with type Ⅰ lesion(1/3).Soft tissue involvement presented in 5 cases(5/10,50.00％),with borderless diffuse slightly low-density,including 2 cases of lesions significantly enhanced after enhancement.Non-contrast MRI showed that the affected bone presented equal T1 or slightly lower T1,mixed T2 or slightly higher T2 signal,while the affected soft tissue were found with equal T1 and slightly higher T2 signal.Conclusion Clinical and imaging findings of KHE involved bone had certain characteristics.

Objective To observe the clinical and CT features of neonatal adrenal cystic neuroblastoma(CNB).Methods Eight newborns with adrenal CNB confirmed by surgical pathology were retrospectively analyzed.The clinical data were recorded,and the plain and enhancement abdominal CT manifestations were observed.Results Among 8 cases,6(6/8,75.00％)were detected with prenatal ultrasound,while 2(2/8,25.00％)were detected after birth with ultrasound,all with single adrenal grand lesion,located half in left and half in right adrenal gland(each 4/8,50.00％).The maximum diameter of CNB lesion was 2.3-6.1 cm,with the median maximum diameter of 4.5 cm.CT showed all 8 lesions(8/8,100％)presented as single localized adrenal grand thick-walled cystic lesion,among which 3(3/8,37.50％)with uniform density within the cysts,3(3/8,37.50％)with internal septum within the cysts,1(1/8,12.50％)with slight floating debris and the rest 1(1/8,12.50％)with both internal septum and floating debris in the cyst.No calcification,cross the midline nor surround blood vessels were observed.Seven(7/8,87.50％)lesions had clear while 1(1/8,12.50％)had unclear boundaries,all mildly compressed surrounding structures.The capsule wall and internal septum of the cysts slightly enhanced after enhancement.Multiple liver metastases occurred in 2 cases.Conclusion Most neonatal adrenal CNB were detected before delivery,which mainly presented as thick-walled cystic mass with clear boundary,accompanied by septa and floating debris,and the cystic wall and septa slightly enhanced after enhancement,and liver metastasis might occur.