Surgical treatment, with removal of the epileptogenic zone, remains the best therapeutic option for patients with pharmacoresistant focal epilepsies. Mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS) is the epileptic syndrome with the best surgical outcome, with up to 60% of patients seizure-free 5 years after the procedure.

The advent of MRI in the 1980s allowed the in vivo identification of HS, a histopathologic diagnosis. The MRI signs of HS are reduction of volume, with or without hyperintense T2-weighted signal, along with abnormal shape and internal structure of the hippocampus. However, in some cases, the MRI signs of HS are subtle and can be missed even by well-trained eyes. So, in the early 1990s, studies demonstrated that the use of methods to quantify the hippocampal volume and signal could increase the in vivo detection of HS. Also, as in other neurological disorders, the quantification of the hippocampal damage, in addition to helping in diagnosis and prognosis,  allows its correlation with different clinical characteristics aiming to improve the understanding of the condition.

Hippocampal volumetry and T2 relaxometry, in the context of MTLE, help to identify subtle structural abnormalities in otherwise nonlesional (MRI-negative) patients, allowing for a shorter and less costly presurgical evaluation of patients with pharmacoresistant MTLE. However, increasing resolution of recent MRI, including the expanding clinical use of higher fields (3T) improved the visual detection of mild volume and signal changes in mesial temporal structures in images acquired with appropriate protocol. This, along with the time-consuming and difficult manual segmentation, have made hippocampal volumetry impractical for clinical use. It was also not clear if the use of hippocampal quantification techniques could still add information to the visual identification of the hippocampal pathology in higher resolution 3T images.

In our study we demonstrated, in a large group of patients with MTLE, that, indeed, the use of a combination of hippocampal T2 relaxometry and automatic hippocampal volumetry in 3T MRI can increase the detection of signs of HS by 28%, with a high concordance with the EEG lateralization.

With the present results it may be possible to rely more on the automated hippocampal quantification tools in the routine clinical setting, particularly for patients with MTLE with normal or unclear MRI by visual analyses. It is worth noting that in our study we proposed a simple and feasible use of the quantification tools: automatic volume and a simple manual signal quantification requiring only a few minutes to be performed.

Although we agree that for research purposes (and in the hands of well-trained researchers) the use of manual hippocampal volumetry has some advantages,¹ it is, however, impractical in the clinical scenario.²

A question that remains is whether the subtle signs of HS detected only by volumetry and relaxometry are also associated with different histopathological substrates of HS, as recently proposed by the International League Against Epilepsy.³ Therefore, our future goal is to compare the results of our hippocampal quantification techniques with postoperative specimens in order to answer this question.

 

References

1. Pardoe HR, Jackson GD. Manual hippocampal volumetry is a better detector of hippocampal sclerosis than current automated hippocampal volumetric methods. AJNR Am J Neuroradiol 2013;34:E114–15
2. Coan AC, Cendes F. Reply. AJNR Am J Neuroradiol 2013;34:E116
3. Blümcke I, Thom M, Aronica E, et al. International consensus classification of hippocampal sclerosis in temporal lobe epilepsy: a Task Force report from the ILAE Commission on Diagnostic Methods. Epilepsia 2013;54:1315–29

 

Read this article at AJNR.org . . .