Clinical diagnosis
Case 150
【Progress】
Two months later, brain MRI depict low signal intensity at the right fornix on T2*WI (Fig. 2). He forgot the explanation of CT findings two months ago and to begin with, he did not remember to take brain CT itself. However, this time, he fully understood the explanation of brain MRI findings and what happened to him.
【Discussion】
Fornix is composed of neural fibers (axons) extending from hippocampus to mammillary body whose neural fibers, then, connect to anterior part of the thalamus (1, 2). Fornix is a crucial part of limbic system and also Papez circuit (2). Fornix is sometimes overlooked on CT and MRI. It exists as a pair at the midline of the brain beneath the lateral ventricle and passes through outside the septum pellucidum.
Left fornix carries information of verbal memory and right fornix carries information of visuospatial memory (2-4) which indicates verbal memory is stocked in the left hippocampus and visuospatial meomory in the right hippocampus. In our patient, he got the right fornix contusion and he did not memorize the scene of falling downstairs and what the physician explained the findings obtained by CT two months ago. However, this time, he fully understood the meaning what the physician explained the findinges obtained by MRI.
Fornix as well as corpus callosum is the midline white matter which is susceptible to involvement of gliobalastoma, malignant lymphoma and Langerhans histiocytosis (2, 5, 6). Further, Wernicke encephalopathy caused by thiamine (vitamin B1) deficiency involves the midline of the cerebrum such as mammmary bodies, periaqueductal gray matter, thalamus and fornix (7). Furthermore, three diseases are listed for atrophy of fornix; herpes simplex encephalitis involves preferentially the mesial temporal lobe via trigeminal nerve ganglion including the limbic system. The atrophy of fornix and hippocampus following herpes simplex encephalitis is sometimes encountered (2); mesial temporal (hippocampal) sclerosis causing epilepsy which is characterized by neural loss and astrogliosis causes the atrophy of hippocampas and fornix (2); Alzheimer disease is characterized by atrophy of entrhino-cotex of hippocampas, amygdala and fornix (2, 8).
As one of the traumatic damages, diffuse axonal injury causd by the rotaional shearing injury is now incresing awareness of the involvement to fornix (2, 9). In our case, we did not have proof of diffuse axonal injury on MRI because it showed the hemorrhage of right fornix alone, indicating the local fornix contusion. Fornix is blood-supplied by minute branches of the anterior commnication artery (2). Infarction and hemorrhage of the fornix are rare. According to the patient history that he fell down from his bed and five days later, fell downstairs from five steps upward, hemorrhagic fornix is believed to have occured from trauma but not from sporadic rupture of the anterior commnicating artery.
【Summary】
We present an eighty five year-old male who experienced dropping down from the bed five days before and falling down from five steps height two days before. Brain CT showed hemorrhage of the right fornix, indicating fornix contusion. It is borne in mind that fornix gets blood supply from minute arteries branched from anterior communicating artery. Fornix is one of the crucial components of limbic system and exists beneath the lateral ventricle and passes through outside the septum pellucidum. Left fornix carries information of verbal memory and right fornix carries information of visuospatial memory. Fornix is susceptible to involvement of gliobalastoma, malignant lymphoma and Langerhans histiocytosis. Further, Wernicke encephalopathy caused by thiamine (vitamin B1) deficiency involves the midline of the cerebrum such as mammmary bodies, periaqueductal gray matter, thalamus and fornix. Fornix atrophy occurs in cases of herpes simplex encephalitis, mesial temporal (hippocampal) sclerosis and Alzheimer disease.
【References】
1.Mark LP, et al. The fornix. AJNR Am J Neuroradiol. 1994;14 (6): 1355-8.
2.Thomas A, et al. The Fornix in Health and Disease: An Imaging Review. RadioGraphics 2011; 31:1107–1121
3.Raslau, FD, et al. Memory Part 3: The Role of the Fornix and Clinical Cases. American Journal of Neuroradiology September 2015, 36 (9) 1604-1608
4.Tucker DM, et al. Memory dysfunction following unilateral transection of the fornix: a hippocampal disconnection syndrome. Cortex 1988;24:465–472
5.Saeki N, et al. Heavily T2-weighted MR imaging of white matter tracts in the hypothalamus: normal and pathologic demonstrations. AJNR Am J Neuroradiol 2001;22(8): 1468–1475.
6.Yoon SS, et al. Retrograde amnesia associated with fornix lymphoma. Eur Neurol 2008; 60(3):155–158.
7.Zuccoli G, et al. Neuroimaging findings in acute Wernicke’s encephalopathy: review of the literature. AJR Am J Roentgenol 2009;192(2):501–508.
8.Copenhaver BR, et al. The fornix and mammillary bodies in older adults with Alzheimer’s disease, mild cognitive impairment, and cognitive complaints: a volumetric MRI study. Psychiatry Res 2006;147(2-3):93–103.
9.Yasuno F, et al. Retrograde temporal order amnesia resulting from damage to the fornix. J Neurol Neurosurg Psychiatry 1999;67 (1):102–105.
2019.6.26