Images below require Macromedia's Flash Player to view

Neuroradiology Case of the Week

Case 105

Deepa Popuri, Leena Ketonen, MD, PhD
and PL Westesson, MD, PhD, DDS

Clinical Presentation: A 37-year-old right-handed female presents with staring spells, paranoia, and olfactory hallucinations. There is clinical suspicion for mesial temporal sclerosis.

Radiological Findings: There is signal and size asymmetry within the hippocampal formations with body of the right hippocampus being smaller than the left. In addition, there is abnormally increased T2 and FLAIR signal within the body of the right hippocampus. There is, however, no evidence for abnormal enhancement after intravenous gadolinium administration. Atrophy of the fornix is demonstrated on the right side, corresponding to the side of hippocampal abnormality. The right mamillary body is also smaller and displays higher signal.

Diagnosis: Mesial temporal sclerosis (MTS)

Discussion: 
Clinical Discussion: Hippocampal pathology is the most common cause of intractable temporal lobe epilepsy. Hippocampal sclerosis occurs in 65% of epilepsy patients in autopsy studies (Jackson). Patients present with memory dysfunction and history of febrile seizure. EEG will reveal localized anterior temporal lobe abnormality [1,2]
     Etiology/Pathology: Mesial temporal sclerosis is characterized by hippocampal sclerosis, gliosis, and cell loss [3]. Internal morphological structure of the hippocampus is disturbed and replaced with gliotic tissue. Neuronal cell loss in the hippocampus most often involves dentate gyrus and the CA1, CA3, and CA4 sections of cornu ammonis. Hippocampal atrophy visualized as volume reduction tends to be more severe with epilepsy duration, history of prolonged or complex febrile seizures, or number of generalized tonic-clonic seizures. Volume reductions in structures ipsilateral to the epilectic focus in hippocampal and extrahippocampal regions may occur, although these abnormalities tend to be less severe than at the focus. Affected sites may include the amygdala, entorhinal cortex, subiculum, parahippocampal gyrus, thalamus, and cerebellum. Atrophy of limbic structures such as fornix and mammillary bodies may occur. Atrophy of the fornix often accompanies hippocampal abnormality, since the fornix serves as the major efferent pathway of the hippocampus [1,4].
     Prognosis/Treatment: Temporal lobe resection with removal of mesial structures or selective amydalohippocampectomy is associated with good outcome. Ninety percent of patients with severe neuron loss will benefit from elimination of seizures after the procedure [2,3].

Neuroimaging Discussion: CT is less sensitive than MRI in detection of hippocampal pathology [5]. Hippocampal assessment in MRI is best performed using two planes, one plane through the body of the hippocampus and the other plane at a right angle to this. The coronal view is most sensitive in detecting volume reduction and T2 signal change while the axial plane can better assess posterior extent of hippocampal abnormality [2,3].
     Hippocampal atrophy is hypointense on T1WI and hyperintense on T2WI. T1WI gives better anatomic detail as to the precise location of abnormality. Note that high signal on T2WI may also represent small tumor, increased CSF space, trauma, or flow artifact (Jackson). It may be difficult to diagnose bilateral abnormality because of the size and shape variability of hippocampal structure [3]. Gradient echo technique (SPGR) is more sensitive than spin echo technique because smaller slice thickness allows for improved gray white matter differentiation. Volume study may reveal atrophic, triangularly shaped hippocampus instead of oval shape. Temporal horn of the lateral ventricle is often enlarged on the side of the atrophic hippocampus [2]. Volume reductions in ipsilateral structures such as the amygdala, mamillary body and fornix may be present [1].
     PET imaging is another useful modality in detection of epileptogenic region in the temporal lobe. During interictal periods, FDG hypometabolism is evident at the focus. This hypometabolism may extend beyond the focus but has not been correlated quantitatively with degree of cell loss. PET offers greater spatial resolution than SPECT, and is therefore the modality of choice in functional imaging [5].

References:

1. Kuzniecky R, Bilir E, Gilliam F et al. Quantitative MRI in temporal lobe epilepsy: evidence for fornix atrophy. Neurology1999;53:496-501.
2. Bronen RA, Chang F, Charles JT, et al. Imaging finding in hippocampal sclerosis: correlations with pathology. AJNR 1991;12:933-940.
3. Jackson GD,Barkovic SF, Duncan JS, Connelly A. Optimizing the diagnosis of hippocampal sclerosis using MR imaging. AJNR 1993;14:753-762.
4. Theodore WH, Gaillard WP. Neuroimaging and progression of epilepsy. Progress in Brain Research 2002;135:305-313.
5. Sperling MR. Neuroimaging in Epilepsy: Recent developments in MR imaging, positron-emission tomography, and single-photon emission tomography. Neurologic Clinics 1993;11:883-903.