What is the most appropriate investigation for a pediatric patient with a head injury and no loss of consciousness, but bruising on the left jaw?

In the context of a pediatric patient with a head injury accompanied by bruising on the left jaw, the most appropriate investigation would be a facial X-ray. This choice is particularly relevant when assessing potential facial fractures, especially considering the bruising, which may indicate underlying trauma to the jaw or facial structures.

Facial X-rays can effectively visualize any fractures or abnormalities in the facial bones, specifically those associated with the jaw area, allowing for a targeted assessment based on the patient's symptoms. They are often employed in cases of suspected mandibular or maxillary injury, enabling the clinician to rule out or confirm an injury that may not be apparent upon physical examination.

While a CT scan is a valuable imaging tool for assessing intra-cranial injuries, particularly in cases involving loss of consciousness or neurological deficits, its use is usually reserved for more severe head trauma or when there are concerning signs of more complex injuries. MRI is generally not indicated in acute trauma situations due to the longer time required for imaging and is not primarily used to assess bony structures like the facial skeleton. An abdominal ultrasound is unrelated to the evaluation of head or facial injuries and would not be an appropriate investigation in this clinical scenario.

Therefore, the facial X-ray aligns well with the need to evaluate