Downbeat nystagmus associated with damage to the medial longitudinal fasciculus of the pons: A vestibular balance control mechanism via the lower brainstem paramedian tract neurons

The paramedian tract (PMT) neurons, a group of neurons associated with eye movement that project into the cerebellar flocculus, are present in or near the medial longitudinal fasciculus (MLF) in the paramedian region of the lower brainstem. A 66-year-old man with multiple sclerosis in whom downbeat nystagmus appeared along with right MLF syndrome due to a unilateral pontomedullary lesion is described. In light of these findings, a possible schema for the vestibular balance control mechanism circuit of the PMT neurons via the flocculus is presented. Damage to the PMT neurons impaired the elective inhibitory control mechanism of the anterior semicircular canal neural pathway by the flocculus. This resulted in the appearance of anterior semicircular canal-dominant vestibular imbalance and the formation of downbeat nystagmus.From the pathogenesis of this vertical vestibular nystagmus, the action of the PMT neurons in the vestibular eye movement neuronal pathway to maintain vestibular balance was conjectured to be as follows. PMT neurons transmit vestibular information from the anterior semicircular canals to the cerebellum, forming a cerebellum/brainstem feedback loop. Vestibular information from that loop is integrated in the cerebellum, inhibiting only the anterior semicircular canal neuronal pathway via the flocculus and controlling vestibular balance

Cerebral Venous Air Embolism due to a Hidden Skull Fracture Secondary to Head Trauma

Cerebral venous air embolism is sometimes caused by head trauma. One of the paths of air entry is considered a skull fracture. We report a case of cerebral venous air embolism following head trauma. The patient was a 55-year-old man who fell and hit his head. A head computed tomography (CT) scan showed the air in the superior sagittal sinus; however, no skull fractures were detected. Follow-up CT revealed a fracture line in the right temporal bone. Cerebral venous air embolism following head trauma might have occult skull fractures even if CT could not show the skull fractures

Body Lateropulsion and Cerebellar Tremor in a Patient with Pontine Infarction

Body lateropulsion is known to be caused commonly by lateral medullary lesions but rarely by pontine lesions. It is also known to be associated with lesions of the dorsal spinothalamic tract or ascending graviceptive pathways. We herein report the case of a 75-year-old woman presenting with contralateral lateropulsion and cerebellar tremor caused by pons infarction. To our knowledge, this is the first case report of pontine infarction causing both lateropulsion and cerebellar tremor. Our case may be helpful in anatomical studies of ascending graviceptive pathways