Carbon monoxide poisoning with isolated bilateral hippocampal involvement

Clinical History

A 16 year-old girl was admitted to hospital because she was found at home unconscious. The anamnesis revealed that stove was used to heat the house overnight. The diagnosis of acute carbon monoxide (CO) intoxication was made with 47% of blood carboxyhemoglobin (COHb) concentration.

Imaging Findings

For the disclosure of presence of central nervous system (CNS) involvement, cranial magnetic resonance imaging (MRI) was acquired. The bilateral hippocampal volume was symmetrically increased. The vasogenic oedema was evident in bilateral hippocampus with hypointensity on T1-weighted images, hyperintensity on T2-weighted images, and no diffusion restriction. The cerebral and cerebellar parenchyma was otherwise normal. The patient was discharged fully healthy following the hospitalization for 1 week. The control brain MRI obtained 3 months later was normal.

Discussion

CO poisoning is the most common cause of accidental poisonings in North America and Europe [1]. Following the clinical suspicion, detection of increased blood COHb level (>5% in non-smokers) is the main diagnostic method for the determination of CO exposure [2]. MRI has been reported to be more sensitive than computed tomography to reveal the presence and extent of CNS involvement [3]. Globus pallidus is most frequently effected intracranial structure; other basal ganglia, cerebral grey and white matter, cerebellum are other regions that are effected with decreasing frequency. In literature, isolated hippocampal involvement has been reported as case reports and occurs very rarely [4].
COHb has oxygen affinity 250 times higher compared to haemoglobin. The poisoning emerges as a result of abundant oxygen-COHb combination that prevents oxidative phosphorylation and ultimately causes ischemic encephalopathy. Patients may present with a variety of symptoms and clinical findings including headache, convulsions, comatose state, and death. The injury of the brain may be as vasogenic oedema or necrosis.
The radiological imaging techniques, particularly the diffusion weighted MRI, are utilized in order to reveal the CNS involvement. When solely the vasogenic oedema is present, the effected regions show symmetrical hypointensity on T1-weighted images and hyperintensity on T2-weighted images. With the additional cytotoxic oedema-cell necrosis, additionally diffusion restriction is detected [5]. In 80% of the cases with CO poisoning, it has been reported that, even though no lesion is detected during the acute phase, in the following 6 months, atrophy and cognitive retardation are detected due to neuronal necrosis and apoptosis [6].
During the treatment, 100% oxygen is applied using either a mask or mechanic ventilation. Thereby, with the increased oxygenation of the tissues, COHb is extracted from the body. The physiological and randomized controlled trials showed that patients benefit from hyperbaric oxygen therapy, but the identification of patients who may benefit is still controversial [7].
The differential diagnosis list of isolated involvement of bilateral hippocampus due to CO poisoning includes infectious (e.g., herpes simplex), metabolic (e.g., hypoglycemia) and vascular pathologies, with the appropriate clinical information and laboratory it is possible to reach the accurate diagnosis.

Differential Diagnosis List

Final Diagnosis

Carbonmonoxide poisoning with bilateral isolated hippocampal involvement

URL:	https://eurorad.org/case/12404
DOI:	10.1594/EURORAD/CASE.12404
ISSN:	1563-4086