Brain herniation in a patient with apparently normal intracranial pressure: a case report
© Dahlqvist et al; licensee BioMed Central Ltd. 2010
Received: 1 April 2010
Accepted: 31 August 2010
Published: 31 August 2010
Intracranial pressure monitoring is commonly implemented in patients with neurologic injury and at high risk of developing intracranial hypertension, to detect changes in intracranial pressure in a timely manner. This enables early and potentially life-saving treatment of intracranial hypertension.
An intraparenchymal pressure probe was placed in the hemisphere contralateral to a large basal ganglia hemorrhage in a 75-year-old Caucasian man who was mechanically ventilated and sedated because of depressed consciousness. Intracranial pressures were continuously recorded and never exceeded 17 mmHg. After sedation had been stopped, our patient showed clinical signs of transtentorial brain herniation, despite apparently normal intracranial pressures (less than 10 mmHg). Computed tomography revealed that the size of the intracerebral hematoma had increased together with significant unilateral brain edema and transtentorial herniation. The contralateral hemisphere where the intraparenchymal pressure probe was placed appeared normal. Our patient underwent emergency decompressive craniotomy and was tracheotomized early, but did not completely recover.
Intraparenchymal pressure probes placed in the hemisphere contralateral to an intracerebral hematoma may dramatically underestimate intracranial pressure despite apparently normal values, even in the case of transtentorial brain herniation.
Elevated supratentorial intracranial pressure (ICP) can cause transtentorial brain herniation, leading to cerebral hypoperfusion, brainstem herniation, and ultimately death, if left untreated . ICP monitoring is, therefore, commonly implemented in patients with neurologic injury and a high risk of developing intracranial hypertension, in order to detect changes in ICP in a timely manner and to induce therapeutic interventions . Measurement of ICP appears particularly important in patients who cannot be clinically evaluated due to sedation .
In this case report, we present a patient who experienced transtentorial brain herniation despite an apparently normal ICP.
Traditionally, intraparenchymal pressure probes are placed in one of the frontal lobes in an attempt to minimize complications . Although some study results have been controversial , a notable amount of evidence indicates that marked and clinically relevant ICP gradients within the supratentorial compartment may exist in patients with neurologic injury [3, 5–7]. ICP gradients of up to 28 mmHg were reported in humans . In contrast to diffuse lesions, interhemispheric ICP gradients were detected in almost half of patients with a focal brain lesion. In most of these cases, ICP was higher in the vicinity of the focal mass and correlated directly with its size [3, 5–7].
The guidelines in our center require that ICP be recorded at the site of the lesion. However, the guidelines were not followed in this case. In our patient, the ICP gradient was so high that "normal" ICP was measured in the right hemisphere while transtentorial herniation of the left hemisphere occurred. The size and location of intracerebral hemorrhage could explain why even a moderate increase in left-hemispheric ICP may have caused transtentorial brain herniation in our patient and did not increase right-hemispheric ICP first. Thirty years ago, Papo et al. suggested that neurological deterioration and even brain herniation may occur in the absence of significant ICP changes in patients with intracerebral hemorrhage . Even though we cannot definitely exclude the possibility, it is unlikely that an artifact of the ICP monitor caused the observed discrepancy of brain herniation in our patient with apparently low ICP. CT images showing a massively swollen left hemisphere with a structurally normal right hemisphere underline this assumption. Furthermore, substantial drifts of intraparenchymal pressure devices usually do not occur immediately after insertion .
Although this report describes a single patient, we believe that relevant lessons for ICP measurement in patients with intracerebral hemorrhage can be drawn from this case. First, placement of an intraparenchymal probe into the hemisphere contralateral to a large intracerebral hemorrhage may grossly underestimate ICP around the hematoma. This can be particularly devastating when hemorrhage occurs in deep brain structures such as the basal ganglia which are anatomically close to the tentorium. Considering experimental study results [11, 12], it must be assumed that placement of the intraparenchymal pressure probe on the ipsilateral side of the lesion would have allowed detection of locally elevated ICP in our patient. Furthermore, one can hypothesize that measurement of ICP through an intraventricular sonde might have rendered even more reliable ICP results than placement of a left-sided intraparenchymal sonde in the presented patient. Since intraventricular sondes record the pressure of the cerebrospinal fluid which distributes equally throughout the supratentorial compartment, it is unlikely that they are prone to recording false low ICPs even if relevant supratentorial ICP gradients are present.
Intraparenchymal pressure probes placed in the hemisphere contralateral to an intracerebral hematoma may dramatically underestimate ICP and render apparently normal values even in the case of transtentorial brain herniation.
Written informed consent for publication of this case report and any accompanying images was obtained from the patient's next of kin. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
magnetic resonance tomography.
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