isolated central nervous system ( cns ) relapse is still a significant cause of morbidity and mortality and can occur in a range of 2 - 6% of patients with acute lymphoblastic leukemia ( all ) despite the improvement in cns - directed therapy . several risk factors such as the initial leukemic involvement of the cns and the presence of t ( 1,19 ) or t ( 9;22 ) have been proposed for cns relapse . the patients with isolated cns relapse are usually asymptomatic , and the blasts are detected in cerebrospinal fluid ( csf ) usually on routine examinations during therapy . leptomeningeal involvement due to invasion of blasts can often be detected by imaging modalities , but pure parenchymal infiltrative mass is an extremely rare presentation of cns disease . herein , we report a leukemic child with isolated cns relapse confirmed by both csf evaluation and cranial imaging showing an extensive intracerebral mass to underline various types of cns involvement of all . a 7-year - old boy presented with fatigue , fever , and generalized bone pain lasting for a month . physical examination yielded cervical and inguinal lymphadenopathies besides hepatosplenomegaly . complete blood count revealed hemoglobin ; 9.5 g / dl , platelet ; 24  10/l and leukocyte count ; 12  10/l with 70% blast on the peripheral smear . bone marrow aspiration confirmed the diagnosis of all - french - american - british ( fab ) l2 type - and common all antigen ( + ) b all with flow cytometry ( cd10 : 89% , cd19 : 82% , cd22 : 94% , and tdt : 38% ) . polymerase chain reaction ( pcr ) showed negative t ( 9;22 ) , t ( 1;19 ) , and t ( 11,14 ) . after the 22 weeks of the therapy , he experienced generalized tonic - clonic convulsion . however , csf evaluation and cranial magnetic resonance imaging ( mri ) showed no involvement . on the 55 week ; lymphoblasts were detected in csf by cytocentrifugation during routine examination . he was retreated with st jude txiiib induction protocol and triple intrathecal ( it ) ( metotrexate - cytarabine and prednisolone ) therapy was performed twice a week until the clearance of the csf . triple it therapy was continued monthly and craniospinal radiotherapy was also added to the protocol . at the end of the treatment on 120 week , he achieved complete remission without blasts in bone marrow and csf . physical examination showed significant decrease in muscle power on the right side of the body , anisocoria , and bilateral papilledema by fundoscopic evaluation . computerized cranial tomography ( cct ) yielded a mass in size up to 6 cm in the largest diameter located in deep white matter of left anterior frontal lobe . csf evaluation showed tdt positive lymphoblasts with high protein level ( 82 mg / dl ) . complete surgical resection was performed , and he gained the function of right extremities dramatically the day after the operation . immunohistochemical staining demonstrated diffuse positivity with cd10 and patchy positivity with tdt . owing to the diagnosis of the second isolated cns relapse , a new chemotherapy protocol was planned , but the family refused the therapy and left the hospital . he presented with decreased muscle power on the right side of the body and headache again 3 months after the operation . new cranial imaging showed the recurrence of the hyperdense lesion with the dimensions of 8  5 cm and midline shift [ figure 1a ] . triple it therapy twice a week was performed till the csf was cleared of blasts , and st jude all relapse protocol was started . the mass begun to decrease in size and was completely shrunken a month later without surgical intervention . cranial computed tomography revealed intraparenchymal mass he completed all relapse protocol and is still in remission with no blast in csf and bone marrow . the mri at the end of the relapse protocol showed bilateral parietal subdural collections and gliotic - atrophic signal changes in left anterior frontal lobe [ figure 1b ] . the presence of lymphoblasts in csf at the diagnosis , traumatic diagnostic lumbar puncture , high initial leukocyte count , t - cell immunophenotype , and pre - b all with t ( 1;19 ) constitute the risk factors of cns relapse . although our patient did not possess any of the aforementioned risk factors , he developed cns relapse 3 times . reported that chemo / radiotherapy resistant residual blasts in csf might be responsible for these relapses . it may be thought that the generalized tonic - clonic convulsion on the 22 week was thought as a clue for the first cns relapse . however , no blasts were detected in csf by cytology and cytocentrifugation . between 22 and 55 weeks of the therapy , triple it therapy was performed at every 2 months and the convulsion did not repeat . this period between the convulsion and cns relapse might be due to additive effects of both anti - epileptic drugs and it therapy . cns leukemia - at the diagnosis or relapse - may develop in various types ; mostly , blasts can be detected in csf without neural tissue involvement . when it is focal , it may mimick parenchymal brain tumors due to local contrast uptake . leukemic cells were defined to firstly infiltrate the walls of superficial arachnoidal veins and subsequently progress into deep arachnoid vessels located in white and gray matter . obstruction of arachnoid villi impedes csf circulation and consequently leads to increased intracranial pressure . at this stage of the progression , patients generally present with some symptoms such as headache , blurred vision , and other neurologic findings , suggesting cns relapse and necessity of csf evaluation . if the patients can not be diagnosed at this stage , blood - brain barrier damage occurs leading to intracerebral leukemic infiltration . in present case , lymphoblasts were detected only in csf without neural tissue involvement at the first cns relapse , but parenchymal mass developed at the second and third relapses . intracerebral mass is more common in patients with acute myeloid leukemia ( aml ) as granulocytic sarcoma and t - cell immunophenotype than those with b - cell all . this is partly due to the relatively more common expression of cd56 - an isoform of the neural adhesion molecule ( ncam ) - in aml and t - cell all . although cd56 staining was negative , parenchymal leukemic infiltration developed twice in our case . to our knowledge , this is the 2 leukemic child who developed intraparenchymal mass as a cns leukemia until now . it should be noted that the present case per se did not have any of the identified risk factors , but he developed three cns relapses , two of which as development of an intracerebral mass .
central nervous system leukemia may present in different ways . however , intraparenchymal mass is extremely rare in childhood leukemia . 
 herein , we report a boy who presented with right hemiparesis and anisocoria 1 year after the cessation of the chemotherapy protocol for acute lymphoblastic leukemia . 
 cranial imaging demonstrated an extensive mass located in the anterior white matter of left frontal lobe , and cerebrospinal fluid examination revealed concomitant lymphoblasts . 
 immunohistochemical staining of the biopsy material showed neoplastic cells with positive cd10 and tdt . 
 complete remission was achieved with chemotherapy alone for a duration of 2 years .