one - third of patients with epilepsy have seizures that are resistant to pharmacological therapy . resective surgery is effective for patients with pharmacoresistant epilepsy who have a localized area of epileptogenic tissue in noneloquent cortex . these masses of disorganized neuronal tissue are usually associated with gelastic seizures , intellectual disabilities , and behavioral changes . tissue destruction can achieve seizure freedom rates ranging from 30 to 50% in mixed adult  pediatric populations . a recent series of 14 patients treated with mri - guided stereotactic laser ablation of hypothalamic hamartomas achieved seizure freedom in 86% with a mean follow - up of nine months . none of these patients suffered focal neurological deficits , neuroendocrine disturbances , or memory losses . we present a young man who underwent mri - guided stereotactic laser ablation of a hypothalamic hamartoma following a right temporal lobectomy for resection of a focal cortical dysplasia . his case illustrates the need to assess for dual pathology in treatment of pharmacoresistant epilepsy and the potential complications of mri - guided stereotactic laser ablation . a 19-year - old right - handed man had attention deficit disorder and treatment - resistant focal epilepsy with weekly seizures ( behavioral arrest , incomprehensible speech , and postictal confusion ) since the age of nine . seizures persisted despite trials with 12 antiepileptic drugs used in up to three - drug combinations , steroids , intravenous gamma globulin , modified atkin 's diet , and a vagus nerve stimulator . on video - eeg , seizures involved bilateral changes evolving more over the right hemisphere . magnetoencephalography showed multifocal bilateral polyspike - and - wave discharges as well as right frontal temporal  occipital discharges . magnetic resonance imaging demonstrated a subtle cortical abnormality in the right insula and frontal operculum , with subtle atrophy of the right fornix and mammillary body . neuropsychological testing targeting delayed memory recall showed story memory delayed recall ( dr ) 50th percentile , list learning dr 75th percentile , and figure copy dr 14th percentile ( table 1 ) . intracarotid amobarbital testing revealed left language dominance and right hemispheric memory impairment ( right hemisphere memory [ left injection ] score : 7/12 ; left hemisphere memory [ right injection ] score : 12/12 ) . when the patient was 17 years old , intracranial eeg monitoring with right hemispheric grids , strips , and depths captured 49 seizures : 32 had broad onset over the right lateral temporal , mesial temporal , frontal , and occipital lobes and insula , while 17 arose from depth electrodes in the right posterior mesial temporal lobe . he underwent resection of the right lateral temporal and mesial cortex , along with the inferior insula and frontal operculum . he remained active in varsity lacrosse , maintained a 3.5 gpa in a competitive high school , had a close circle of friends , and was accepted to his first - choice college . a brief neuropsychological screen revealed list learning dr 50th percentile , figure copy immediate recall ( ir ) , and dr 18th percentile ( table 1 ) . when he was 18 , repeat mri demonstrated the right temporal lobectomy and now an 8-mm hypothalamic hamartoma on the right , not recognized on multiple previous mri studies ( fig . in retrospect , the patient now admitted that his seizures both before and after the lobectomy included mirthless laughter . he was referred to a center with expertise at mri - guided stereotactic laser ablation and underwent this procedure . he reported feeling as though he was in a dream with events happening in a disjointed fashion . three weeks postoperative , he required hospitalization for agitation and suicidal ideation and was diagnosed with a severe amnestic syndrome with confabulation . video - eeg monitoring captured several complex partial seizures with impaired responsiveness and bilateral ictal discharges . repeat mri showed not only successful ablation of the hamartoma but also unexpected contrast enhancement that crossed the midline involving the bilateral medial mammillary bodies and adjacent anteromedial left thalamus ( fig . neuropsychological testing ( table 1 ) revealed a dense anterograde amnesia ( story memory ir 1st percentile , dr 0.1 percentile ; list learning ir 2nd percentile , dr 1st percentile ; and figure copy dr 1st percentile ) , with impaired attention and processing speed . neuropsychological testing ( table 1 ) eight months after hamartoma ablation demonstrated improved attention , concentration , and immediate recall but severe deficits in delayed recall ( story memory ir 13th percentile , dr 2nd percentile ; list learning ir 18th percentile , dr <  0.1 percentile ; and figure copy memory dr <  0.1 percentile ) . clinically , he has a disabling amnestic syndrome . he deferred his college education plans and is unable to drive because of ongoing seizures . they cause medically refractory epilepsy associated with some combination of gelastic and other seizure types , cognitive impairment ( epileptic encephalopathy ) , and behavioral changes including aggression . removal or destruction of the hamartoma can control seizures and improve cognition , especially in children . magnetic resonance imaging - guided laser ablation is a minimally invasive technique that uses mri - guided placement and application of thermal heat to destroy a tissue focus . among 14 patients with medically refractory epilepsy due to hypothalamic hamartoma who underwent stereotactic laser ablation , 11 ( 79% ) became seizure - free after a single treatment ; another patient became seizure - free after a second ablation ( 12/19 ; 86% ) . there were no surgical complications previously associated with traditional operative techniques , such as neuroendocrine disturbances , visual changes , or hemiparesis . our patient 's case is the first reported serious complication of mri - guided stereotactic laser ablation of hypothalamic hamartoma . the presence of bilateral postoperative changes in the mammillary bodies suggests that the laser ablation may have been sufficient to account for his deficits . one group   reported on a patient who also presented with such dual pathology : a 35-year - old man who underwent removal of a left temporal subarachnoid cyst and resection of temporal neocortex for treatment of intractable complex partial seizures . similar to our patient , targeted questioning revealed that he had always experienced short outbursts of  genuine  laughter , which he had not felt was abnormal . postoperative mri , ictal pet , and spect revealed an 8-mm hypothalamic hamartoma retrospectively present on preoperative scanning . three other patients underwent partial or total resection of a hypothalamic hamartoma and later had temporal lobectomies . in two of these cases , there were no pathological abnormalities found in the resected temporal lobe tissue ; pathology in the third case is not described . secondary epileptogenesis was postulated as the cause of the temporal lobe focus after removal of the hypothalamic hamartoma . transient memory loss ( two months ) following lesionectomy of the hamartoma was seen in one of the cases but did not worsen further after the temporal lobectomy . by contrast , a fourth patient had mesial temporal sclerosis and a 5-mm hypothalamic hamartoma and presented with epigastric rising sensation , dizziness , and fear . video - eeg recording localized seizure onset to the right temporal lobe , and she became seizure - free after a right temporal lobectomy . gelastic seizures not only are associated with hypothalamic hamartomas but also occur with seizure foci due to diverse pathologies , including focal cortical dysplasias in the temporal , frontal , and parietal lobes . our case was unique in having both a hypothalamic hamartoma and pathologically confirmed focal cortical dysplasia . the hypothalamic hamartoma was missed at several academic medical centers but was present before the right temporal lobectomy , although subtle . mild brain shift from the original resection widened the appearance of the third ventricle and made the hamartoma obvious . our patient 's original seizures may have been attributable to the right temporal focal cortical dysplasia , the hypothalamic hamartoma , or a network involving the two abnormalities . anterograde amnesia can result from disruption of mesial temporal lobe structures or the mesial diencephalon . diencephalic ( mammillary bodies and medial thalamus ) pathology can result from alcoholism , malnutrition , infection , trauma , or infarct [ 1719 ] . however , many cases show damage involving other portions of the memory network , including the hippocampus . our case is unique since anterograde amnesia resulted from a right temporal lobectomy followed by an ablative lesion that unfortunately extended into both medial mammillary nuclei with greater involvement contralateral to the lobectomy . it is likely that the bilateral nature of the temporal  diencephalic lesion led to amnesia . this case illustrates the potential for severe memory deficits following laser ablation of hypothalamic hamartomas . since many children who undergo this procedure are very young or have moderate - to - severe intellectual disability , it may be difficult to assess memory function in these individuals . it is worthwhile to consider dual pathology in epilepsy and the potential morbidity of mri - guided laser ablation of hypothalamic hamartomas , especially in a patient with a prior temporal lobectomy .