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Hippocampal Sulcus Remnant Cysts
KEY FACTS
Terminology
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Synonyms: Hippocampal remnant cyst, hippocampal sulcal cavities
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Cyst or string of cysts along residual cavity of primitive hippocampal sulcus
Imaging
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String of cysts along lateral margin of hippocampus
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Cysts follow cerebrospinal fluid signal on all MR sequences
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T2: Hyperintense
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FLAIR: Complete suppression
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T1WI C+: No enhancement
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Top Differential Diagnoses
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Mesial temporal sclerosis
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Choroid fissure cyst
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Arachnoid cyst
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Dysembryoplastic neuroepithelial tumor
Pathology
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Represent partially unfused hippocampal sulcus
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Embryology
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Primitive hippocampal fissure is formed as cornu ammonis and dentate gyrus fold on each other to form cleft
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Cornu ammonis and dentate gyrus then fuse, leaving shallow hippocampal sulcus
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Defects in this fusion cause remnant cysts within primitive sulcus
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Clinical Issues
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Incidental finding, not associated with pathology
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Often observed on high-resolution imaging for evaluation of seizure patients (10-15%)
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Have been noted to enlarge with temporal lobe atrophy in Alzheimer disease
Axial graphic of the normal temporal lobe shows a string of cysts within the lateral hippocampus, along the residual cavity of the primitive hippocampal sulcus
, representing hippocampal sulcus remnant cysts. These incidental findings have a characteristic appearance.
, representing hippocampal sulcus remnant cysts. These incidental findings have a characteristic appearance.
Axial T2WI in an asymptomatic patient shows prominent hippocampal sulcus remnants
in both medial temporal lobes.
in both medial temporal lobes.
Axial T2WI MR shows small hyperintense cysts in the hippocampus
. These unfused remnants of the embryonic hippocampal sulcus present as cerebrospinal fluid-like cysts, appearing as a “string of beads” coursing through the hippocampus.
. These unfused remnants of the embryonic hippocampal sulcus present as cerebrospinal fluid-like cysts, appearing as a “string of beads” coursing through the hippocampus.
Axial FLAIR MR in the same patient shows complete suppression of the hippocampal sulcus remnant cysts
. The string of beads appearance is typical of these common normal variants. They have been found to enlarge in patients with temporal lobe atrophy.
. The string of beads appearance is typical of these common normal variants. They have been found to enlarge in patients with temporal lobe atrophy.
TERMINOLOGY
Abbreviations
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Hippocampal sulcus remnant cysts (HSRC)
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