The Value Of Longer Delayed Multiphasic Contrast-Enhanced MRI In The Diagnosis Of The Necrotic Nodule Of The Liver And Its Differential Diagnosis From Other Mimic

BackgroundThe solitary necrotic nodule of the liver(SNNL)is a rare benign tumor-like lesion.So far,the etiology of SNNL is unclear.Trauma,the infection of parasites,hemangioma,allergic reaction caused by malignant tumors and ischemia are suspected to be related to the onset of SNNL.SNNL has apparent benign behavior.The size of SNNL can stay stable for a long period of time or gradually regress to complete disappearance.The treatment of SNNL is mainly conservative therapy.Thus,the definite diagnosis of SNNL can avoid unnecessary surgery.The clinical symptoms and signs of SNNL are unspecific and none of laboratory tests can be used for its definite diagnosis.At present,MRI is regarded as the most valuable method for the diagnosis of SNNL among the radiographic modalities.However,the characteristic manifestations of SNNL on MRI are still controversial.Some authors argue that the absence of enhancement on arterial phase,venous phase and delayed phase of contrast enhanced MRI is characteristic while other authors believe that the presence of peripheral rim-like enhancement on delayed phase and the absence of central enhancement on all enhanced phases is specific.Those contradictive conclusions and unspecific clinical data has caused that based on the clinical symptoms,history,radiographic manifestations and laboratory tests the suspected rate of SNNL before surgery is only 7.8%.Despite of the controversy of characteristic imaging manifestations,the pathology of SNNL is specific,which is featured by central complete coagulative necrosis surrounded by hyalinized fibrous capsule infiltrated with chronic inflammatory cells like plasma cells,monocytes and lymphocytes.Given the close relationship between fibrous tissue and enhancement on delayed phase and the delayed time is no more than 5min on routine contrast enhanced MRI,we infer that the absence of peripheral enhancement is due to the relatively short delayed time.Thus,we apply the longer delayed multiphasic contrast enhanced MRI with the delayed time prolonged to 2h to obtain the specific imaging manifestations and increase the definite diagnosis rate of SNNL.ObjectivesTo explore the 'value of longer delayed multiphasic contrast-enhanced MRI in the diagnosis of solitary necrotic nodule of the liver(SNNL)and its differential diagnosis through obtaining specific imaging findings of SNNL by using longer delayed contrast-enhanced MRI and compare those findings with 3 main mimic hepatic diseases.Methods16 patients with SNNL confirmed by pathology underwent plain and contrast-enhanced triphasic CT and multiphasic MRI with the delayed time of 3min,5min,10min,15min,30min,1h and 2h after contrast bolus injection.Meanwhile,23 patients with mimic lesions including 7 patients with 8 hepatocellular carcinomas(HCCs),5 with 5 intrahepatic cholangiocarcinomas(iCCs)and 11 with hepatic metastatic lesions were set as the control group.Those patients also received plain and multiphasic contrast-enhanced MRI examination.However,further scan in most patients was waived when the peripheral wash-out of the lesion was observed.CT and MRI features of the lesion including number,location,shape,size,density,signal intensity,enhancement degree,and peripheral wash-in and wash-out time were evaluated by two experienced radiologists.ResultsAmong the 16 lesions identified in the 16 patients with SNNL,4(25%)and 8(50%)showed mild peripheral rim-like enhancement on conventional delayed phase CT and MRI(delayed time<5 min).With the delayed time of contrast-enhanced MRI being prolonged,the enhancement degree of the tumor periphery/septa increased gradually.When it was up to 1 hour,all lesions(100%)represented moderate to marked peripheral rim-like enhancement with internal hypointensity.In the control group,all HCCs,iCCs and most metastatic lesions represented moderate or marked rim-like enhancement in conventional MRI delayed phase(delayed time<5 min).However,the peripheral wash-out in 7 HCCs(87.5%)and almost all except 3 metastatic lesions appeared at 10-15min after the injection of contrast agents and that in 1 iCC(20%)emerged at 30-min and the rest 4(80%)at 1h.In addition,the peripheral washout in iCCs and metastatic lesions was usually accompanied by centeral patchy enhancement.ConclusionsLonger delayed MRI with a delayed time of 1-or 2-hour plays an important role in the diagnosis of SNNL and the differential diagnosis of it from mimic diseases,which reveals the specific imaging characteristic of SNNL as pronounced peripheral/septal enhancement with internal hypointensity.In contrast,the peripheral enhancement of HCCs,iCCs and metastatic lesions disappeared on 1h-delayed phase.If no enhancement presents in the lesion during the whole longer delayed period,the diagnosis of SNNL can be excluded.