Basal Nuclei Anatomy and Imaging

Overview

This lecture reviews the anatomy of the basal ganglia (more accurately, basal nuclei) using various neuroimaging techniques, focusing on structure, location, and clinical relevance.

Orientation and Major Landmarks

• The basal ganglia are best seen at the level of the lateral and third ventricles on axial brain images.
• The internal capsule separates the caudate nucleus (medially) from the putamen and globus pallidus (laterally).
• The thalamus lies on either side of the third ventricle.

Basal Nuclei Anatomy

• The basal nuclei (basal ganglia) are gray matter structures within the CNS and include the caudate, putamen, globus pallidus, subthalamic nucleus, and substantia nigra.
• The caudate nucleus has a head (anterior/bulky), body (follows the lateral ventricle posteriorly), and a thin tail (down to temporal horns).
• The putamen is separated from the caudate by the anterior limb of the internal capsule and is wedge-shaped.
• The caudate and putamen together form the neostriatum (corpus striatum or dorsal striatum), acting as a functional unit.
• The putamen and globus pallidus are collectively called the lentiform nucleus (lens-shaped), though not as functionally unified as the striatum.
• The globus pallidus is divided into external and internal segments, best seen on coronal sections.

Additional Nuclei and Midbrain Anatomy

• The subthalamic nucleus lies just below and slightly anterior to the thalamus; difficult to see on standard MRI.
• The substantia nigra, containing dopamine fibers, separates the red nucleus from the cerebral peduncles; best viewed on susceptibility-weighted imaging (SWI).
• Red nuclei are only present at the level of the superior colliculi in the midbrain.
• Important cisterns: quadrigeminal (posterior to colliculi), interpeduncular (between cerebral peduncles), and ambient (surrounding the midbrain).

Imaging Modalities and Clinical Relevance

• On CT, basal nuclei appear lighter than white matter; loss of gray-white differentiation can indicate early infarct.
• The caudate head is supplied by anterior cerebral artery branches and is vulnerable to ischemia.
• MRI (especially T1 and SWI) shows better soft tissue contrast and detail of basal nuclei compared to CT.
• Certain diseases cause increased T1 signal in the globus pallidus and subthalamic nucleus.

Key Terms & Definitions

• Basal ganglia/basal nuclei — Gray matter structures within the CNS involved in motor control.
• Striatum/Neostriatum — Functional unit of caudate nucleus and putamen.
• Lentiform nucleus — Anatomical unit comprising the putamen and globus pallidus.
• Subthalamic nucleus — Nucleus located below the thalamus, part of motor circuitry.
• Substantia nigra — Dopamine-rich midbrain nucleus, affected in Parkinson’s disease.
• Internal capsule — Major white matter tract separating key basal nuclei structures.

Action Items / Next Steps

• Review labeled MR and CT brain images to practice identifying basal nuclei.
• Learn the basic blood supply of the basal nuclei for clinical correlations.
• Prepare for exam questions on basal nuclei anatomy and their imaging appearance.