Lateral Sulcus

The lateral sulcus (Sylvian fissure) separates the frontal lobe (superior) from the temporal lobe (inferior). The insula lobe is located in depth of the lateral sulcus and is covered by the cortex from the frontal lobe, temporal and parietal (operculum)

The lateral sulcus, also referred to as the Sylvian fissure or lateral fissure, is one of the most prominent parts of the human brain(1)

The lateral sulcus is a deep cleft in each hemisphere that divides the frontal and parietal lobes from the temporal lobe. 

The insular cortex lies deep within the lateral sulcus. This part of the brain plays a role in sensory experience and emotional valence(2)

The lateral sulcus is one of the earliest-developing sulci (fissures) of the human brain that first appears around the 14th gestational week(3).

Anatomy of the Lateral Sulcus

The fissure courses medially to form the ‘stem’ of the lateral fissure, which is known as the Sylvian cistern. The Sylvian cistern passes the middle cerebral artery and its major branches(4).

The lateral sulcus’ anatomy on the brain’s lateral surface divides into three rami (branches of nerves): anterior horizontal, anterior ascending, and posterior(5)

The anterior horizontal ramus extends into the inferior frontal gyrus (ridge), running anteriorly and horizontally. The anterior ramus separates the pars orbitalis from the pars triangularis.

The anterior ascending ramus runs vertically into the same gyrus and defines the inferior frontal gyrus’ pars triangularis portion. This portion is anterior to the ascending ramus and posterior to the pars opercularis.

The anterior ascending ramus also separates the pars triangularis from the pars opercularis. 

The posterior ramus extends posteriorly and slightly superiorly for approximately 8cm and divides into the posterior ascending and posterior descending rami(6).

The posterior ascending ramus lies within the supramarginal gyrus of the inferior parietal lobule.

The lateral sulcus contains the transverse temporal gyri, which is part of the primary area and below the auditory cortex’s surface.

Due to a phenomenon known as the Yakovlevian torque, the lateral sulcus is less curved and often longer on the brain’s left hemisphere than on the right(7). The lateral sulcus is also located near the Sylvian point.

Meanwhile, the area lying around the lateral sulcus is often referred to as the perisylvian cortex(8). This region is the site for phonetic processing, syntactic, and semantic detection(9).

Surrounding Structures

The temporal lobe’s superior surface forms the lateral sulcus floor and continues with the superior temporal gyrus. The temporal lobe’s superior surface is also bounded medially by the circular sulcus, which surrounds the insula(10).

The insula is a lobe of the cortex that makes up the expanded floor of the lateral sulcus. Meanwhile, the limen insulae (insula’s anterior end) is continuous in the stem of the lateral sulcus. 

The temporal lobe’s posterior part blends into the parietal lobe above and the occipital lobe behind. 

A straight line drawn from the parieto-occipital sulcus to the preoccipital notch defines the occipital lobe’s anterior border on the lateral aspect of the hemisphere(11)

From the midpoint of this straight line, a horizontal line passes forward to the lateral sulcus to separate the temporal from the parietal lobe.


Arachnoid Cyst

Arachnoid cysts are commonly benign and asymptomatic lesions that can occur within the central nervous system(12)

These cysts are most frequently located in the middle cranial fossa, enclosing and widening the lateral fissure. Arachnoid cysts can be classified into three types based on their size: Galassi I, II, and III(13).  

Arachnoid cysts may arise due to the congenital splitting of the arachnoid layer with an accumulation of cerebrospinal fluid (CSF) within this potential space. 

The cyst wall consists of flattened arachnoid cells that form a thin translucent membrane. There is no epithelial lining and no solid component(14).

In medical images, arachnoid cysts are characterized as well-circumscribed cysts, with an imperceptible wall displacing adjacent structures and following the CSF pattern. These cysts can also have a remodeling effect on the adjacent bone(15)

Epidermoid Cyst

Epidermoid cysts (also known as epidermoid tumors) are benign congenital lesions that contain cellular debris, keratin, and cholesterol(16)

The cysts’ usual locations are the parasellar region and cerebellopontine angle, Sylvian fissure, suprasellar region, cerebral and cerebellar hemispheres, and lateral and fourth ventricles. These cysts are rarely located in the brain stem. 

Epidermoid cysts found in the posterior fossa usually arise in the lateral subarachnoid cisterns. Studies suggest that these cysts develop between the third and fifth gestational week from ectodermal remnants(17)

The tumors grow slowly in discreet silence sustained over a multitude of years. Common symptoms experienced by patients are headache and seizures(18)

In a case report, magnetic resonance imaging (MRI) of the brain exhibited an irregular lesion in the right Sylvian fissure with extensions in the frontal and temporal opercula, the parasellar region, and the crural cistern(19).


• Harnsberger HR, Osborn AG, Ross JS, Moore KR, Salzman KL, Carrasco CR, Halmiton BE, Davidson HC, Wiggins RH. Diagnostic and Surgical Imaging Anatomy: Brain, Head and Neck, Spine. 3rd ed. Salt Lake City, Utah. Amirsys. 2007.
• Bourjat P, Veillon F. Imagerie radiologique tête et cou. Paris, Vigot. 1995.
• Gouazé A, Baumann JA, Dhem A. Sobota. Atlas d’Anatomie humaine. Tome 3. Système nerveux central, système nerveux autonome, organe des sens et peau, vaisseaux et nerfs périphériques. 1er éd. Paris, Maloine. 1977.
• Kahle W, Cabrol C. Anatomie. Tome 3: Système nnerveux et organe des sens. 1er éd. Paris, Flammarion. 1979.

19 sources

  1. Bui, T., & Nguyen, J. (2019). Neuroanatomy, Cerebral Hemisphere.
  2. Uddin, L. Q., Nomi, J. S., Hébert-Seropian, B., Ghaziri, J., & Boucher, O. (2017). Structure and function of the human insula. Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society, 34(4), 300.
  3. Jee G. Chi; Elizabeth C. Dooling; Floyd H. Gilles (January 1977). “Gyral development of the human brain”. Annals of Neurology. 1 (1): 86–93. doi:10.1002/ana.410010109
  4. Bui, T., & Nguyen, J. op. cit.
  5. Ibid.
  6. Ibid.
  7. Ibid.
  8. Norbury, C. F., Tomblin, J. B., & Bishop, D. V. (Eds.). (2008). Understanding developmental language disorders: From theory to practice. Psychology press.
  9. Hurschler, M. A., Liem, F., Jäncke, L., & Meyer, M. (2013). Right and left perisylvian cortex and left inferior frontal cortex mediate sentence‐level rhyme detection in spoken language as revealed by sparse fMRI. Human brain mapping, 34(12), 3182-3192.
  10. Bui, T., & Nguyen, J. op. cit.
  11. Ibid.
  12. White ML, M Das J. Arachnoid Cysts. [Updated 2020 Oct 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from:
  13. ibid.
  14. Ibid. 
  15. Heier, L. A., Zimmerman, R. D., Amster, J. L., Gandy, S. E., & Deck, M. D. (1989). Magnetic resonance imaging of arachnoid cysts. Clinical imaging, 13(4), 281-291.
  16. Shah, A., Makkiyah, F., & Goel, A. (2016). Sylvian fissure epidermoid cyst presenting with intention tremor. Asian journal of neurosurgery, 11(2), 174–175.
  17. Ghartimagar, D., Shrestha, M. K., & Ghosh, A. (2020). Recurrence of ruptured intracranial epidermoid cyst–A rare case report and presentation. International Journal of Surgery Case Reports, 76, 310-314.
  18. Shah, A., Makkiyah, F., & Goel, A. op. Cit.
  19. Ibid. 
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