Noncontrast CT scan of the head.
Question: What is this black line?
Answer: The right transverse cerebral fissure.
Comment: The transverse cerebral fissures are part of the subarachnoid space. At the level of the above image,
the transverse cerebral fissures open into the superior cerebellar cistern.
After development of the interhemispheric fissure, the transverse cerebral fissures are the next
major fissures formed in the developing telencephalon.
The transverse cerebral fissures are the axis around which the enlarging temporal lobes curve forward
producing the characteristic reverse C-shaped configuration to structures connecting the frontal
and parietal lobes with the temporal lobe. At the most lateral part of the transverse cerebral fissure,
vessels penetrate the medial wall of the lateral ventricle to form the choroid plexus. This line of
penetration extends from the foramen of Monro to the tip of the inferior horn of the lateral ventricle
along the medial wall of the ventricle. This defect in the medial wall of the ventricle, which is filled with
the choroidal vessels and their supporting tissues, is called the choroidal fissure. See the image below.
As the brain develops, the transverse cerebral fissure provides the separation between the medial temporal
lobe and the adjacent portion of the diencephalon, the thalamus. In the adult brain,
the transverse cerebral fissure is sometimes referred to as the retropulvinar cistern.
It is continuous anteriorly with the perimesencephalic cistern/ambient cistern.
Same image as above
Red arrows: transverse cerebral fissures
Green arrows: choroidal fissures