The triangle of Guillain and Mollaret, also known as the dentatorubro-olivary pathway, has three corners 1:
Rubro-olivary fibres descend from the parvocellular division of each red nucleus along the central tegmental tracts to reach the capsule (amiculum) of the ipsilateral inferior olivary nucleus (ION). From the ION, olivocerebellar fibres cross the contralateral inferior cerebellar peduncle to reach cerebellar cortex, then pass from cerebellar cortex to the contralateral dentate nucleus. Dentatorubral fibres then ascend via the contralateral superior cerebellar peduncle, decussate in the midbrain, and return to the original red nucleus 1.
Note that no direct connecting tract is present between the inferior olivary nucleus and contralateral dentate nucleus 1.
Lesions of the superior cerebellar peduncle lead to contralateral hypertrophic olivary degeneration. Lesions of the central tegmental tract lead to ipsilateral hypertrophic olivary degeneration. Lesions of the olivocerebellar fibres lead to contralateral cerebellar atrophy.
Potential clinical manifestations include palatal myoclonus and a dentatorubral upper limb tremor (Holmes tremor).