Topics

Topic

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Collateral trigone

The collateral trigone is a triangular region of the lateral ventricle located at the junction of the body, occipital horn, and temporal horn. It lies in the posteroinferior portion of the lateral ventricle, adjacent to the posterior part of the hippocampus and the lateral wall of the atrium. This area is traversed by the choroid plexus, which contributes to cerebrospinal fluid production, and is bordered by the fibers of the collateral eminence and calcarine sulcus.

The collateral trigone serves as an anatomical landmark in neuroimaging, helping to assess ventricular size, cortical atrophy, hydrocephalus, and mass lesions. Its shape and size can vary, and asymmetry may indicate congenital anomalies, tumors, or post-traumatic changes.

Function

  • Houses part of the choroid plexus, contributing to cerebrospinal fluid production

  • Serves as a ventricular landmark for neuroimaging and neurosurgical planning

  • Helps maintain ventricular architecture and cerebrospinal fluid flow

  • Adjacent structures participate in memory and visual processing

Synonyms

  • Trigone of lateral ventricle

  • Atrium of lateral ventricle

  • Collateral atrium

MRI Appearance

T1-weighted images:

  • Appears as a CSF-filled hypointense region relative to surrounding brain parenchyma

  • Choroid plexus is isointense to mildly hyperintense, easily distinguishable from CSF

  • Borders of the trigone are defined by adjacent temporal and occipital white matter

T2-weighted images:

  • The collateral trigone is hyperintense due to CSF signal

  • Choroid plexus remains intermediate signal intensity, allowing clear differentiation

  • Useful for evaluating ventricular dilation, lesions, or adjacent white matter abnormalities

STIR (Short Tau Inversion Recovery):

  • CSF remains high signal, while edema or pathology in surrounding parenchyma appears hyperintense

  • Helps detect inflammatory, neoplastic, or post-traumatic changes

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal trigone shows enhancement of the choroid plexus only, with no enhancement of CSF

  • Pathological conditions (tumors, ependymomas, choroid plexus papilloma) appear as focal or nodular enhancement

CT Appearance:

  • Appears as a CSF-density triangular region at the junction of body, occipital horn, and temporal horn

  • Choroid plexus is slightly hyperdense relative to CSF, clearly visible on non-contrast CT

  • Excellent for assessing ventricular enlargement, hemorrhage, calcifications, or mass lesions

MRI images

Collateral trigone mri axial image