Online Quiz

CASE 2 ( Closed )

History :
Clinically suspected case of encephalitis. Patient on ventilator. MR imaging showed the following.


Review the imaging series and give your diagnosis.
What are the differentials diagnosis?

Please see the answer below.



Diagnosis: Brain Death

Teaching Points:
On MR, loss of flow void in the intracranial ICA, central and tonsillar herniation, and diffuse brain swelling along with absence of any cerebral vessels above the level of the supraclinoid portions of the ICA on MR angiograms are findings suggestive of brain death. In particular, MR angiography provides a non-invasive and reliable method for the diagnosis of brain death.


Brain death is the state of irreversible cessation of all cerebral and brain stem functions resulting from edema and massive destruction of brain tissue despite continued cardiopulmonary activity maintained by advanced life-support systems and mechanical ventilation. The increasing refinement and implementation of organ transplantation procedures requires an unequivocal diagnosis of brain death for legal and moral reasons. The method of diagnosing brain death should be free of error, easilyand quickly performed, and verifiable.

The diagnosis of brain death can usually bemade by physical examination to detect coma,the absence of cephalic reflexes, and the absenceof spontaneous respiration, and by a flat EEG. Established clinical criteria usuallysuffice, but even objective tests such as theEEG may be inaccurate in comatose patientsowing to drug-induced hypothermia, intoxication,and shock. Conventionally, serial EEGsand radionuclide perfusion studies, either planarimaging or SPECT, have been used to confirmthe diagnosis of brain death in an appropriateclinical setting. The absence ofcerebral blood flow is generally accepted as adefinite sign of brain death. The reasonfor the cessation of cerebral blood flow afterbrain death is uncertain. Although an intracranialpressure higher than the mean arterial pressureis not the sole explanation for the absence.

Several authors have documented the MRfindings in patients with brain death, includingOrrison et al, who identified six signs:
(a) transtentorial and foramen magnum herniation,
(b) absence of the intracranial vascular flowvoid,
(c) poorgray matter/white matter differentiation,
(d) no intracranial enhancement,
(e) carotidartery enhancement (the intravascular enhancementsign), and
(f) prominent nasal andscalp enhancement (the "hot nose" sign).

We did not perform contrast-enhanced MRimaging, we also noted the first three signs in ourpatient. However, these three findings aloneshould not be considered indicative of braindeath, since transtentorial and foramen magnumherniation as well as poor gray matter/white matterdifferentiation may also be observed in patientswith severe hypoxic brain damage in theabsence of brain death.

Absence/reversal of end-diastolic flow inophthalmic, central retinal arteries are features.

Nuclear Medicine Findings

  • Absent supra-, infratentorial uptake ("light bulb"sign).
  • Increased extracranial activity ("hot nose" sign).

In brain death, regardless of the cause, increased intracranial pressure decreases cerebral blood flow. This phenomenon leads to cytotoxic edema and the progression of brain swelling. Finally, compression of the entire network of intracranial arteries is observed. As such, paradoxical and irreversible brain death occurs. Diffuse hyperintensities on DWI and ADC drop may be non-specific and can occur in other situations, such as bilateral carotid artery occlusion. With other findings, diffuse hyperintensities on DWI and ADC drop can be a finding of brain death.

The cortical vein sign on GRE is defined as visualization of both cerebral hemisphere cortical veins. Similar imaging findings are encountered in acute stroke, subarachnoid hemorrhage, cortical vein thrombosis, vascular malformations such as developmental venous anomalies and arteriovenous malformations, and patients under general anesthesia.


Brain Death Mimics

  • Severe hypoxic brain damage.
  • Near-drowning.
  • Trauma.
  • Cocaine.


  1. Brain Death: MR and MR Angiography Kiyoshi Ishii, TakehideOnuma, Toshibumi Kinoshita, GenzoShiina, MotonobuKameyama, and Yasuko ShimosegawaJones KM, Barnes PD. MR diagnosis of brain death. AJNR Am J Neuroradiol1992;13:65–66
  2. Aichner F, Felber S, Birbamer G, Luz G, Judmaier W, Schmutzhard E. Magnetic resonance: a noninvasive approach to metabolism, circulation, and morphology in human brain death. Ann Neurol1992;32:507–511
  3. Orrison WW Jr, Champlin AM, Kesterson OL, Hartshorne MF, King JN. MR 'hot nose sign' and 'intravascular enhancement sign' in brain death. AJNR Am J Neuroradiol1994;15:913–916