Sylvian Fissure

One of the most prominent features of the brain.

The sylvian fissure is the space between the frontal, parietal and temporal opercula and the insula and extends from the basal to the lateral surface of the brain. It is constituted by a superficial part and a deep part.

  1. The superficial part presents a stem (on the basal surface) and three rami (on the lateral surface).
    1. The stem extends medially from the semilunar gyrus of the uncus to the level of the tip of pars triangularis. This is where the stem divided into anterior horizontal, anterior ascending and posterior rami.
    The transition between the basal and lateral parts of the sylvian fissure can therefore be considered as located at the level of the pars triangularis.
  2. The deep part is divided into an anterior operculoinsular compartment (on the basal surface) and a lateral operculo-insular compartment (on the lateral surface).
    1. The anterior operculoinsular compartment consists of an anterior opercular compartment and an anterior insular compartment.
      1. The anterior opecular compartment is located between the opercular portion of the lateral and posterior oribital gyri on the frontal side and the upper part of the anterior portion of the planum polare on the temporal side.
      2. The anterior insular compartment is restricted only to the narrow space posterior to the sphenoid ridge between the frontal and temporal lobes, in front of the insular pole (sphenoidal compartment), but also extends upward over the anterior surface of the insula, between the posterior surfaces of the lateral, posterior, and medial orbital gyri anteriorly and the anterior surface of the insula posteriorly.
      The anterior insular compartment communicates medially with the carotid cistern, also called the sylvian vallecula.
    2. The lateral operculo-insular compartment is formed by two narrow clefts:
      1. the opercular cleft between the opposing lips of the fronto-parietal and the temporal opercula
      2. the insular cleft, which has a superior limb between the insula and the frontoparietal opercula and an inferior limb between the insula and the temporal operculum.

The gyri that constitute the fontal and parietal opercula of the sylvian fissure are, posteriorly to anteriorly: the supramariginal gyrus, the postcentral gyrus and the precentral gyrus; the pars opercularis, pars triangularis and the pars orbitalis. The gyri that constitute the temporal operculum of the sylvian fissure are posteriorly to anteriorly:

  1. the planum temporale
  2. the Heschl's gyrus
  3. the planum polare.

Each gyrus on the fronto-parietal opercula is related to its counterpart on the temporal side:

  1. the supramarginal gyrus is in contact with the planum temporale.
  2. the postcentral gyrus is related to the Heschl's gyrus.
  3. the precentral gyrus, pars opercularis, pars triangularis, and the pars orbitalis are related to the planum polare.

The site on the posterior ramus of the sylvian fissure where the postcentral gyrus meets the Heschl's gyrus is projected in the same coronal plane as the external acoustic meatus.

The medial wall of the lateral insular compartment is the insula or the island of Reil, which can only be seen when the lips of the sylvian fissure are widely seperated.