Table 2 Overview of the most common variants and pathologic entities centred in and around the hippocampus
From: “Unforgettable” – a pictorial essay on anatomy and pathology of the hippocampus
Clinical characteristics | Imaging characteristics | Differential diagnosis | |
|---|---|---|---|
Sulcal remnant cysts | Asymptomatic | CSF iso-intense cyst in the hippocampal fold | / |
Choroid fissure cysts | Generally asymptomatic, rarely seizures or symptoms due to mass effect when large | CSF iso-intense cyst in the choroid fissure | / |
Incomplete hippocampalinversion | Observed in asymptomatic patients and patients with epilepsy, not considered an epileptogenic focus | Globular or pyramidal shape of the hippocampus with normal signal intensity, usually unilateral and left-sided | / |
Alzheimer’s disease | Gradual cognitive decline, usually starts with short-term memory problems | Gradual bilateral volume-loss of the hippocampus and associated mesiotemoral cortex. | Other dementia syndromes, asymmetric temporal atrophy in frontotemporal dementia |
Mesial temporal sclerosis | Complex partial epilepsy | Volumeloss and increased T2 signal intensity of the hippocampus with blurring of the internal structure, bilateral in up to 15%. | / |
Limbic encephalitis | Subacute onset of confusion, seizures, amnesia, behavioural changes, etc. | Uni- or bilateral mesiotemporal cortical swelling and increased signal intensity, diffusion restriction and patchy enhancement possible, evolves to atrophy. | HSV encephalitis, seizure-induced abnormalities |
Herpes simplex encephalitis | Acute onset of fever, headache, seizures, hallucination, personality changes, etc. | Usually starts with unilateral mesiotemporal cortical swelling and increased T2 signal intensity, generally spreads bilaterally. Diffusion restriction, gyral enhancement and petechial hemorrhages possible. | Early stage: limbic encephalitis, seizure-induced abnormalities |
Ganglioglioma | Complex partial epilepsy | Typically (40%) well-defined cortical/corticosubcortical cystic mass with an enhancing nodule. Solid T2-hyperintense mass with variable enhancement also possible. Calcifications in 30%. | DNET |
DNET | Complex partial epilepsy | Typially multicystic cortical/corticosubcortical lesion with peripheral FLAIR hyperintensity (bright rim sign). Enhancement in 30%, calcifications in < 20%. | Ganglioglioma |
Transient global amnesia | Retrograde amnesia lasting < 24 hours | One or more uni- or bilateral intrahippocampal punctiform diffusion-restrictive foci. | More extensive in acute arterial ischemic stroke, generally with other infarcted areas in involved vascular territories |
Acute arterial ischemic stroke | Depends on the extent of the infarction and the vascular territory involved | T2-FLAIR hyperintensity and diffusionrestriction of the hippocampal head in anterior choroidal artery infarction and variable invovement of the entire hippocampus in posterior cerebral artery infarction, generally with other areas of infarction in the involved vascular territories. | / |
Seizure-induced abnormalities | Recent seizure, postictal state or status epilepticus | FLAIR hyperintensity with or without diffusion restriction of the hippocampus | Limbic encephalitis, HSV encephalitis, infarction |