Is there a role for unilateral hippocampal sparing?

There is some lateralization of hippocampus function which may impact decision making.

The left hippocampus seems to play more of a role in episodic verbal memory, while the right plays more of a role in spatial processing. Our neurosurgeon has told me before that a left hippocampectomy is much worse than a right.

https://www.ncbi.nlm.nih.gov/pubmed/27542320

https://www.ncbi.nlm.nih.gov/pubmed/16904344

There is no level one evidence to support unilateral hippocampal sparing; however, I believe it is a reasonable consideration for those patients not amenable to SRS, but with one or more lesions within one hippocampal avoidance zone, but no lesions in close proximity to the other.

We offer this to select patients at our institution, with appropriate consent with regard to current limitations in the existing prospective data.

One should keep in mind that isolated failure within a spared hippocampus is not the end of the world, as SRS can be used to salvage these lesions with a reasonable expectation of reduced deleterious cognitive effect compared to irradiation of the entire HC.

For many decades, it has been common to remove one hippocampus in patients with intractable seizures. Functional outcomes are remarkably good*. However, in 1953, a surgeon removed *both* hippocampi in a young man with seizures arising from both hippocampi. That patient (labeled H.M., his real initials, in the era before HIPAA) went on to have a tragic and most remarkable life, becoming the most famous patient in the history of neuroscience. Completely worth a quick read of this obituary by Larry Squire, an eminent neuroscientist: PMID 19146808.

Yes, I do unilateral sparing for patients with mets only near/in one hippocampus. I see no serious harm to sparing one hippocampus, and there is ample reason to think it could be useful to have one sp...

Related - newer data showing the association between cognitive outcomes (MMSE only) and left, rather than right, hippocampal dose in GBM patients receiving conventionally fractionated vs short course RT. Might provide additional motivation for sparing at least left hippocampus when both are not feasible. Full disclosure that I'm not a CNS specialist but this has influenced my planning approach for e.g., some challenging skull base cases. Would be curious to know what the CNS experts on this thread think.

Yang et al., PMID 36273738

I would also pose the following question, again as a non-CNS specialist. The hippocampus is, as far as I know, not a 'compartment' distinct from the rest of the brain from the standpoint of tumor spread. I'm not ...

Our institution does not offer unilateral hippocampal sparing because the phase III NRG-CC001 trial of WBRT plus memantine without (WBRT+M) or with hippocampal avoidance (HAWBRT+M) excluded patients with lesions within 5mm of either hippocampus. Per Gondi et al in the 2018 ASTRO abstract, neuro-cognitive failure (NCF) was defined as a decline using the reliable change index on at least one of the following tests: Hopkins Verbal Learning Test-Revised, Trail Making Test, or Controlled Oral Word Association. At 6 months the NCF failure rates following WBRT+M vs. HA-WBRT+M were 69.1% (61.8-75.3%) vs. 58.0% (50.2-64.9%).