January 2023 – Neuropathology and Forensic Pathology

The decedent is a 52-year-old man with a history of atherosclerotic cardiovascular disease, diabetes mellitus type 2, and hypertension who was witnessed to become unresponsive and was pronounced shortly after arrival to the emergency department. 

Figure 1

What do the lesions of the brainstem most likely represent?

  • Unilateral subdural hematoma
  • Rapid sodium correction
  • Fixation artifact
  • Internal capsule infarct

The correct answer is ...

Internal capsule infarct.

The image provided shows atrophy of the right cerebral peduncle, pons, and medulla. The decedent in this case had a history of a large remote infarct with right middle cerebral artery (MCA) distribution, which involved the right posterior limb of the internal capsule, causing a residual left motor deficit. The atrophy seen in our picture is a consequence of Wallerian degeneration of the corticospinal tract (CST), later highlighted on histology with LBF-PAS stains.

The corticospinal tract is the major pathway providing voluntary motor function. It originates primarily from the frontoparietal cortices, including the primary motor cortex, secondary motor area, and somatosensory cortex, which come together to form bundles that travel through the internal capsule and cerebral peduncles. The bundles then travel ipsilaterally down to the brainstem. As the corticospinal tract continues to travel down into the medulla, 75% to 90% of the fibers decussate to the contralateral side via the pyramidal decussation, and then continue to travel down the spinal cord to provide innervation to the distal extremities and muscle groups.

It has been shown that the extent of the infarct’s injury to the hemispheric course of the CST predicts the extent of remote tissue loss in the ipsilateral cerebral peduncle and distally, likely resulting primarily from axonal degeneration of the CST distal to the site of injury.

The distribution and gross appearance of the lesion in our picture makes the other choices less likely.


  1. Mark VW, Taub E, Perkins C, Gauthier LV, Uswatte G, Ogorek J. Poststroke cerebral peduncular atrophy correlates with a measure of corticospinal tract injury in the cerebral hemisphere. AJNR Am J Neuroradiol. 2008 Feb;29(2):354-8. doi:10.3174/ajnr.A0811. Epub 2007 Nov 16. PMID: 18024577; PMCID: PMC8119009. 
  2. Natali AL, Reddy V, Bordoni B. Neuroanatomy, Corticospinal Cord Tract. [Updated 2022 Aug 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535423/
  3. Ellison, D. (2013) Neuropathology: A reference text of CNS pathology. Edinburgh: Mosby. 

Fabiola Righi, D.O.

Resident, Anatomic and Clinical Pathology
Mayo Clinic

R. Ross Reichard, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Associate Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.