The fine structure of the axonal torpedo in Purkinje cells of the human cerebellum.

Axonal torpedoes on Purkinje cells of the cerebellum have been observed at electron microscopic level in the case of a 5-year-old boy suffering from juvenile astrocytoma present in the roof of the fourth ventricle and cerebellar hemisphere. The axon torpedo is characterised by a central accumulation of disoriented neurofilaments, which displace the mitrochondria and endoplasmic reticular elements to the periphery. The mitochondria are small and densely staining with longitudinally arranged cristae and are intimately associated with the smooth endoplasmic reticulum that occurs as stacked complexes. Multivesicular and lamellar bodies, typical of degenerating axons, are not consistently seen and this indicates that axon torpedoes are more likely to represent a regenerating state within the nerve fibre than a degenerative condition.