Pathophysiology of Brainstem Lesions Due to Overdrainage
Overdrainage in hydrocephalus therapy is a common shunt complication responsible for many different side effects. Especially an association with an impairment of upper brainstem structures causing symptoms of a dorsal midbrain syndrome (DMS) has already b
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Abstract Overdrainage in hydrocephalus therapy is a common shunt complication responsible for many different side effects. Especially an association with an impairment of upper brainstem structures causing symptoms of a dorsal midbrain syndrome (DMS) has already been described. Yet apart from these known mesencephalic lesions, we found several more brainstem signs and symptoms resulting from overdrainage. Parinaud’s syndrome was diagnosed in all six patients examined; moreover, parkinsonism, memory disturbances, fluctuations in the level of consciousness, and hypothalamic dysfunctions could be detected in five of six patients. In addition hypersalivation combined with peripheral facial nerve palsy and blepharospasm occurred in two patients each, respectively. We postulate an upward herniation of the midbrain into the tentorial notch causing a secondary aqueductal stenosis as causal. An obstructed Sylvian aqueduct and the occurrence of shunt failure can lead to a bulging or enlargement of the third ventricle resulting in diencephalic lesions. If combined with fourth ventricle outlet occlusion, secondary aqueductal stenosis aggravates the situation with a fourth ventricle entrapment. Symptomatology and proposed pathophysiology are presented. Keywords Hydrocephalus • Overdrainage • Brain stem lesions • Upward herniation • Dorsal midbrain syndrome • Fourth ventricle entrapment • Parinaud’s syndrome • Hypersalivation • Blepharospasm • Facial nerve palsy
Introduction Dorsal midbrain syndrome (DMS), also known as Parinaud’s syndrome, Pretectal syndrome, Sylvian aqueduct syndrome, or Koerber–Salus–Elschnig syndrome [9], is a common clinical entity associated with hydrocephalus and shunt malfunction: Overdrainage as well as underdrainage can both be responsible for typical eye movement abnormalities and pupil dysfunctions [1, 2, 9, 15]. In constract, DMS combined with more complex clinical signs such as parkinsonism, mental disturbances, and fluctuations in the level of consciousness – a constellation called global rostral midbrain dysfunction [1, 2, 16] – has not yet been described as a consequence of overdraining shunts. Hypothalamic disorders and deeper brainstem lesions such as cranial nerve failures [6] have not so far been mentioned in the literature either. The initial pathophysiological event is a brainstem upward herniation due to overdrainage resulting in direct lateral midbrain compression in the tentorial notch [4, 5]. The direct impact leads to mesencephalic lesions, and further augmented reduction of cerebrospinal fluid (CSF) can cause a secondary aqueductal stenosis [7]. Such preconditions combined with shunt failure – e.g., ventricular catheter obstruction resulting from overdrainage [1, 2, 8, 12, 15] – may result in a third ventricle enlargement. If an obstruction of fourth ventricle outlets (foramina of Luschka and Magendie) also emerges (e.g., congenitally or functionally) [3], its entrapment [3, 6, 10, 11, 13] could be the logical consequence resulting in direct compression on nearby brainstem structure
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