Is the uncus a part of the temporal lobe and a rostral extension of the parahippocampal gyrus?

The Uncus as a Rostral Extension of the Parahippocampal Gyrus

Yes, the uncus is indeed a rostral extension of the parahippocampal gyrus and is part of the temporal lobe. 1

Anatomical Relationship and Structure

The uncus is an important anatomical structure in the medial temporal lobe with significant clinical relevance. Its anatomical relationships can be described as follows:

• The uncus forms the most anterior and medial portion of the parahippocampal gyrus in the temporal lobe 1
• It has a complex three-dimensional structure with distinct segments:
  • An anterior segment facing the cistern of Sylvius, internal carotid artery (ICA), and middle cerebral artery (MCA) 2
  • An apex that points toward the oculomotor nerve and posterior communicating artery 2
  • A posterior segment with inferior and posteromedial surfaces 1

Anatomical Relationships

The uncus has important relationships with surrounding structures:

• Medial relationships:

  • Posterior cerebral artery (P2A segment) inferiorly
  • Anterior choroidal artery superiorly
  • Optic tract 2

• Lateral relationships:

  • Amygdala (intraventricular)
  • Head of the hippocampus 1

• Clinical significance:

  • The uncus is adjacent to the tentorial edge where the third cranial nerve passes
  • Mass lesions or intracranial bleeding can force the uncus through the tentorial notch, causing compression of the third nerve 3

Functional Considerations

The uncus, as part of the medial temporal lobe structures, has important functional implications:

• It is part of the limbic system involved in memory processing
• Lesions in this area may lead to temporal lobe epilepsy 4
• Surgical approaches to this region must consider preservation of function, particularly in language-dominant temporal lobes 4

Clinical Relevance

The anatomical position of the uncus has significant clinical implications:

• Uncal herniation: When intracranial pressure increases, the uncus can herniate through the tentorial notch, compressing the third cranial nerve and causing a characteristic third nerve palsy 3

• Third nerve palsy manifestations:

  • Ptosis
  • Limitation of eye movement (affected muscles: medial rectus, superior rectus, inferior rectus, inferior oblique)
  • Pupillary dilation (if pupil-involving) 3

• Surgical considerations:

  • In temporal lobe epilepsy surgery, the uncus may be resected as part of an anterior temporal lobectomy or selective amygdalohippocampectomy 5
  • Selective resection of the uncus and amygdala with preservation of the hippocampus may be performed in cases with focal lesions 4

The uncus represents an important anatomical landmark in neuroanatomy and neurosurgery, with its position as the rostral extension of the parahippocampal gyrus making it clinically significant in conditions affecting the medial temporal lobe.