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Median sulcus of rhomboid fossa

The median sulcus is a thin, longitudinal groove located along the midline of the rhomboid fossa, which forms the floor of the fourth ventricle of the brainstem. It extends from the caudal to rostral ends of the fossa, dividing it into symmetrical right and left halves. The median sulcus serves as an important anatomical landmark for identifying adjacent structures such as the median eminence, medial eminences, sulci limitans, and cranial nerve nuclei.

It is most prominent in the pontine and medullary regions, helping to delineate motor and sensory columns of cranial nerve nuclei during neuroimaging. The sulcus is composed of thin neural tissue, and its visualization on imaging requires high-resolution MRI, as it is not normally appreciated on conventional CT.

Function

  • Serves as a midline anatomical landmark in the floor of the fourth ventricle

  • Divides the rhomboid fossa into right and left halves

  • Assists in identifying cranial nerve nuclei and pathways

  • Guides neurosurgical orientation and planning

Synonyms

  • Sulcus medianus

  • Midline groove of fourth ventricle floor

  • Median groove of rhomboid fossa

MRI Appearance

T1-weighted images:

  • The median sulcus appears as a thin, low signal intensity (hypointense) line along the midline of the rhomboid fossa

  • Adjacent neural tissue shows intermediate signal, providing subtle contrast

  • Rarely altered in pathology unless there is congenital malformation or mass effect

T2-weighted images:

  • Appears slightly hypointense compared to surrounding CSF and neural tissue

  • Helps in delineating the midline from adjacent median eminences and sulci limitans

  • High-resolution T2 may show subtle changes in cases of brainstem atrophy or demyelination

STIR (Short Tau Inversion Recovery):

  • Maintains low signal, while adjacent edema or inflammatory changes may appear hyperintense

  • Useful for detecting brainstem lesions, infarcts, or demyelinating plaques

T1 Post-Contrast (Gadolinium-enhanced):

  • Normally, the median sulcus does not enhance

  • Pathology affecting the floor of the fourth ventricle (tumor, infection, vascular malformations) may demonstrate focal enhancement, altering the sulcus contour

CT Appearance:

  • The median sulcus is usually not directly visible on CT due to low contrast between soft tissues

  • High-resolution CT may demonstrate indirect midline alignment of the fourth ventricle floor

MRI images

Median sulcus of rhomboid fossa mri axial image