Cranial trauma or a head injury was a term used for when a person was hit on the head violently or suffered from an injury from hitting their head. This could result in brain damage or cerebral trauma.
In 2267, Dr. Leonard McCoy suggested the head injury Montgomery Scott had recently received as a possibility for his memory loss while on Argelius II. (TOS: "Wolf in the Fold")
In 2365, Doctor Katherine Pulaski was able to exclude a head injury as the reason for the unconsciousness of the doppelgänger of Jean-Luc Picard. (TNG: "Time Squared")
In 2366, Beverly Crusher ruled out cranial trauma as the cause of Patahk's neural pathway degeneration due to the absence of it. (TNG: "The Enemy")
When Commander William T. Riker was undercover on a mission on Malcor III in 2367, she suffered from head injuries he gained during an escape attempt out of the Sikla Medical Facility. (TNG: "First Contact")
In 2369, Doctor Julian Bashir examined Chief Miles O'Brien after he had been found to be suffering from aphasia. Bashir could not find any signs of cranial trauma, which, along with a stroke, was usually a possible cause of aphasia. It was later discovered that O'Brien had contracted aphasia from a device planted on the station in 2351 by Bajorans when it was under Cardassian Occupation. (DS9: "Babel")
In 2371, a representation of Benjamin Sisko that Bashir encountered in his mind following a Lethean telepathic attack told a nurse to give a patient with cranial trauma inpedrezine after treatment with an osteogenic stimulator. (DS9: "Distant Voices")
In 2373, Commander Chakotay suffered from a head injury after he crash landed on a planet in the Nekrit Expanse. (VOY: "Unity")
Later that year, The Doctor's "daughter" Belle hit her head playing parrises squares and suffered severe cranial trauma that compromised her brain stem and motor cortex. (VOY: "Real Life")
In 2374, Seven of Nine suffered from a severe head injury after she received a bullet into her head, a centimeter next to her brain. (VOY: "The Killing Game")
In 2375, B'Elanna Torres suffered cranial trauma amongst other injuries while running holoprograms with the safety protocols turned off. (VOY: "Extreme Risk")
In an alternate timeline, Chakotay told Seska about retaking the USS Voyager while suffering from a head injury. (VOY: "Shattered")