Fornix damage from solitary subependymal giant cell astrocytoma causing postoperative amnesic syndrome

Abstract

A 24-year-old right-handed woman with well-controlled insulin-dependent diabetes mellitus presented with a 1-week history of vomiting. She also gave a 1-year history of intermittent generalized headaches without obvious features of raised intracranial pressure. Neurological examination was normal. Structural brain imaging showed hydrocephalus secondary to an intraventricular heterogeneous mass lesion which compressed the left frontal horn (Figure 1) but without any brain parenchymal lesions or signal change. At operation, tumour was found to have invaded the left fornix but spared the thalamus and caudate nucleus. Histologically the lesion was moderately cellular with both ganglionic and astrocytic type cells, without evidence of mitosis or necrosis; appearances consistent with a subependymal giant cell astrocytoma. Neither the patient nor her family had any history of cutaneous stigmata of tuberous sclerosis. Postoperatively, it became apparent to care staff that the patient had short-term memory problems, repeatedly asking the same question and needing to be reminded about activities to perform. Minimental state examination (MMSE) 2 weeks postoperatively was 14/30. This rose to 24/30 by 10 weeks, and on the Addenbrooke's Cognitive Examination-Revised (ACE-R; Larner, 2007), a more detailed bedside test of cognitive function, she scored 75/100 (Table 1), with evidence of impaired delayed recall for verbal material (ACE-R memory subscore 17/26), and also for visual material (ad hoc object recall test 0/10), with recognition better than recall. There was impaired verbal fluency for both letter and category (ACE-R fluency subscore 3/14). Reassessed 9 months later, almost 1 year after tumour excision, the patient and her family noted continuing subjective improvement in memory but she needed external memory aids to remind herself of appointments, and remained vague about happenings in the year before her surgery, suggesting some possible retrograde memory impairment. She was now at ceiling on the MMSE (30/30) and on ACE-R scored 88/100 (Table 1) with improved delayed recall for verbal material (ACE-R memory subscore 21/26) and visual material (ad hoc object recall test 4/10). Verbal fluency for letter and category was also improved (ACE-R fluency subscore 8/14).