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Crural cistern

The crural cistern is a cerebrospinal fluid (CSF)-filled subarachnoid cistern located at the base of the brain. It lies lateral to the midbrain, specifically between the medial aspect of the temporal lobe and the cerebral peduncle. This cistern acts as an important anatomic space through which several critical neurovascular structures pass, including portions of the posterior cerebral artery, the basal vein of Rosenthal, and cranial nerve III (oculomotor nerve). Understanding its imaging characteristics is important for the evaluation of various pathologies involving the basal cisterns.

Synonyms

  • Ambient cistern (often used interchangeably, though some anatomists differentiate the two; the crural cistern is typically considered the anterior part of the ambient cistern)

  • Lateral mesencephalic cistern (less commonly)

  • Cistern of the cerebral crus

Function

  • Contains cerebrospinal fluid (CSF), helping to cushion and protect adjacent brain structures.

  • Provides a pathway for the passage of key neurovascular structures:

    • Posterior cerebral artery (PCA) segments

    • Basal vein of Rosenthal

    • Oculomotor nerve (cranial nerve III)

  • Serves as a space that can be involved in the spread of pathology (e.g., subarachnoid hemorrhage, infections, or tumors) around the midbrain and temporal lobe.

MRI Appearance

  • T1-weighted Images

    • Appears hypointense (dark), similar to other CSF-filled spaces.

    • Neurovascular structures within the cistern may appear as small, linear, or dot-like areas of intermediate signal intensity.

    • In cases of subarachnoid hemorrhage, acute blood may cause a slight increase in signal intensity.

  • T2-weighted Images

    • Appears hyperintense (bright), consistent with the signal of CSF.

    • Vessels and nerves may be seen as low signal (flow voids) within the bright CSF.

    • Pathologies such as cysts or tumors may alter normal hyperintensity.

  • FLAIR (Fluid-Attenuated Inversion Recovery)

    • Normally, the crural cistern appears hypointense (dark), as CSF is suppressed on FLAIR.

    • Abnormal FLAIR hyperintensity in this region suggests pathology (e.g., blood, infection, proteinaceous material).

CT Appearance

  • Non-contrast CT

    • Appears as a low-density (dark) CSF-filled space lateral to the midbrain and medial to the uncus of the temporal lobe.

    • Adjacent arteries may be faintly visible as curvilinear structures within or around the cistern.

    • Acute blood in subarachnoid hemorrhage appears hyperdense (bright) within the cistern.

    • Effacement or obliteration of the cistern may indicate mass effect or increased intracranial pressure.

MRI images

crural cistern mri 3t axial image

CT image

Crural cistern CT axial anatomy image -img-00001-00001