Preserved Cognition After Right Hemispherectomy

PRACTICAL IMPLICATIONS

Consider the potential for the perseveration of cognitive function after complete right hemispherectomy in a previously healthy adult.

There is controversy regarding the unique contributions of the right and left hemispheres for human cognition. The right hemisphere is believed to play an important role in “nonverbal” cognitive abilities, such as visuospatial processing.¹ However, the necessity of the right hemisphere for other aspects of cognition has been challenged by the relative preservation of intellectual functioning after right hemispherectomy among children and, more rarely, adults with epilepsy because of congenital or early-onset right hemisphere pathology.^2,3 The preservation of normal or near-normal cognition in these remarkable cases is often attributed to the capacity of the left hemisphere for early functional reorganization during development to compensate for cognitive functions that would have involved the right hemisphere in the absence of pathology. Cases of hemispherectomy in adults with normal development are exceptionally rare but could further inform our understanding of the necessity of the right hemisphere for various aspects of cognition.

Case

CB is a right-handed (left-handed mother and maternal grandmother) woman and former retail manager with 14 years of formal education. She had no neurologic or psychiatric history before the onset of an ischemic stroke at the age of 29 that was presumed secondary to a hypercoagulable state in the context of pregnancy and previous infertility treatments. The right internal carotid was occluded with infarction of the right middle, anterior, and posterior cerebral artery distributions. At initial presentation, she had a dense left-sided hemiplegia with no movement of the upper or lower limb with complete loss of sensation on the left; her NIH stroke scale score was 19. She was drowsy but able to understand and participate in discussions regarding consent for an emergent right craniectomy and hemispherectomy, where only a small disconnected right occipital pole was retained. In the days after surgery, she was described as alert, cooperative, and having normal language and interactions with her providers. Prominent neurologic symptoms included left-sided hemiparesis and left homonymous hemianopsia. On discharge from inpatient rehabilitation 2 months after the stroke, she was also noted to have severe deficits in visuospatial ability, milder disturbances in organization and problem-solving, and intact expressive language and reading comprehension.

She was subsequently evaluated at age 34; on interview, she stated that, since the stroke, she had started her own business, was living independently, and raising her child with assistance. She was experiencing chronic central poststroke pain, fatigue, and impulsive shopping but was without any other major psychiatric sequelae. Her examination was notable for limited mobility of the left upper extremity, and she was unable to complete a Grooved Pegboard Test. She was able to ambulate independently with a hemiparetic gait, and she reported some sensation in the left limbs, including itching.

Neuropsychological test performances (data collected 5.3 and 7.8 years after the onset of the stroke; figure)⁴ were notable for normal performance on most tests, including on most nonverbal tests, such as the Block Design test, the Matrix Reasoning test, the Visual Puzzles test, the Judgment of Line Orientation test, the Benton Visual Retention test, the Spatial Span test, and the Faces I and II tests. In addition, she performed within normal limits on several tests of executive functioning, including the Wisconsin Card Sorting test, part B of the Trail Making test, the Color-Word Interference test, and the Similarities test (a test of abstract verbal reasoning and comprehension of implied meanings). Regarding attention, she performed within normal limits on the Line Cancellation test, a test of hemispatial inattention (neglect), and there was no evidence of hemispatial inattention on other neuropsychological tests. Focused and complex attention were within normal limits on parts A and B of the Trail Making Test, respectively.

Figure. Right Hemispherectomy Image and Neuropsychological Data.

The posthemispherectomy brain is shown from an anterior view (left-most panel) as reconstructed from MRI (scan occurred in the chronic epoch, 5.6 years after stroke) along with 3 axial T1 images (right 3 panels, with approximate Montreal Neurological Institute z coordinate listed). Performances on an extensive battery of neuropsychological tests are displayed with scores transformed into standardized Z-scores showing the number of SDs from the mean of a normative reference group. Most test scores fell within the average range (i.e., within normal limits).

Discussion

CB represents a rare case of right hemispherectomy in an adult with normal development and the absence of previous right hemisphere pathology. An important limitation of this case study is that there is not a detailed record of her neuropsychological status immediately after the hemispherectomy with repeated assessments during rehabilitation. A comparable case with a left hemispherectomy in a previously healthy and normally developing adult would also be useful to further clarify the respective roles of each hemisphere.⁵ However, the relative preservation of our patient's performance on standardized cognitive testing in the chronic epoch raises intriguing questions about the functions of the right hemisphere, the measurement of such functions, and the potentially under-recognized ability of the left hemisphere to compensate for right hemisphere dysfunction, even in adulthood, likely through a combination of plasticity and degeneracy/redundancy in cognitive functions.^6,7

Appendix. Authors

Study Funding

This study was supported by the National Institute of General Medical Sciences (T32GM108540), the National Institute of Neurological Disease and Stroke (1 R01 NS114405-01), the National Institutes of Mental Health (1P50 MH094258; 1 R21 MH120441-01), and the Kiwanis Foundation.

Disclosure

The authors report no disclosures relevant to the manuscript. Full disclosure form information provided by the authors is available with the full text of this article at Neurology.org/cp.