Nucleus of the tractus solitarius metastasis: relationship to respiratory arrest?

A 52-year-old woman with metastases in brain and bone had clinical and radiological response to therapy but died about 10 weeks after diagnosis. General autopsy failed to identify a primary neoplasm or an anatomic cause of death. Investigation of sudden respiratory cessation was a consideration when undertaking an anatomic study of the brain.

Review of patient records and careful examination of the brain following autopsy were carried out.

The patient had terminal episodes of hypersomnia but episodes of sleep apnea were not observed. She received no respiratory support and no respiratory difficulties were recorded until she was pronounced dead at 7 a.m. Autopsy revealed metastatic adenocarcinoma in a pattern suggestive of a primary pulmonary neoplasm, including multiple cerebral metastases, although no significant pulmonary lesions of any type were found. A 0.2 cm metastatic adenocarcinoma was found in the nucleus of the tractus solitarius (NTS). No other tumor was present in the brain stem.

Unilateral destruction of the NTS in the medulla would have severely disturbed the most critical point of convergence of autonomic and voluntary respiratory control and of cardiocirculatory reflexes in the central autonomic network. It is postulated that this caused respiratory arrest during a state transition from sleeping to waking. Few metastases to the medulla are reported, most are relatively large, and several have caused respiratory symptoms before death. The very small metastasis in our patient could be the direct anatomic cause of death, and as such it is an unusual complication of metastatic disease of which clinicians should be aware. It is speculated that dysfunction of direct NTS connections to the pons or of connections passing close to the metastatic deposit resulted in terminal hypersomnia.