Bidirectional transynaptic degeneration after resection of brainstem pilocytic astrocytoma.

Abstract

Dear Editor, We would like to report the case of a 12-year-old boy who had undergone surgery for a brainstem pilocytic astrocytoma occupying the fourth ventricle (Fig. 1a). He underwent excision of the tumour by bilateral telovelar approach. Postoperative magnetic resonance imaging (MRI) showed dubious tumour remnants, with no other findings of interest (Fig. 1b) Although he had been discharged in good clinical condition, he was readmitted 4 months later due to a progressive ataxia, diplopia, dysarthria and left hemiparesis of 1 week’s evolution. After readmission, he experienced a deterioration of his neurological condition, with palatal and lingual paraesthesia, fasciculations in the lower limbs, myoclonus in the upper limbs, and a progressive deterioration of the level of consciousness. He underwent subsequent brain MRI, which showed hyperintense T2 lesions at the mesencephalic level in the red nucleus, presenting a clear progression in size (Fig. 1d, e), and a hyperintense T2 lesion with slight increase in volume and asymmetry in the right anterolateral region of the medulla (Fig. 1f), consistent with the theoretical position of the inferior olivary nucleus. In combination, these findings were highly suggestive of hypertrophic olivary degeneration (HOD). Even more strikingly, the serial MRI showed T1 hypointense images (Fig. 1g, h, i, j, k) and hyperintense on T2 images (not showed) at the bilateral dentatothalamocortical pathway level, consistent with ascending degeneration. The patient suffered a cardiorespiratory arrest and eventually died 3 weeks after being re-admitted. Neuronal degeneration secondary to the loss of afferent stimulation may be apparent in various areas of the nervous system, such as the optic pathways and the dorsal root [9, 10]. HOD is a form of transynaptic degeneration causing primarily hypertrophy rather than atrophy of the inferior olivary nucleus that occurs with a delayed fashion and secondarily to lesions with varied aetiologies occurring at the anatomical connections in the dentato-rubroolivary tract, also known as the Triangle of GuillainMollaret [2, 4–6, 8–10]. It contains a connection from the dentate nucleus to the ipsilateral red nucleus through the superior cerebellar peduncle. The fibres descend from the red nucleus through the central tegmental tract to connect to the inferior olivary nucleus. The inferior olivary nucleus sends its fibres through the inferior cerebellar peduncle towards the Purkinje fibres in the contralateral cerebellar cortex, which send their connections to the ipsilateral dentate nucleus, thereby closing the circuit (Fig. 1c). The most important clue for diagnosis is the detection of initial pathological changes in the dentato-rubro-olivary tract [9, 10] (the theoretical location of the red nucleus in our case). Symptoms commonly detailed are palatal tremor, Holmes tremor, ocular myoclonus, paraesthesia, ataxia, dysartria, diplopia, hemiparesis, low limb spasticity, hypoesthesia and dysmetria [9, 10]. In our case, the involvement of the dentatothalamocortical pathway is particularly important from the imaging perspective. Its anatomical relationships have been well defined due to its implications for cerebellar mutism [1, 3, 6, 7]. The efferent fibres originating in the dentate nucleus leave the I. J. Gilete-Tejero :M. Rivero-Garvia : F. J. Marquez-Rivas Paediatric Neurosurgery Unit, Neurosurgery Department, Virgen del Rocio and Virgen Macarena University Hospitals, Seville, Spain