Second-impact syndrome and a small subdural hematoma: an uncommon catastrophic result of repetitive head injury with a characteristic imaging appearance

Abstract

There have been a handful of previously published cases of athletes who were still symptomatic from a prior head injury, and then suffered a second injury in which a thin, acute subdural hematoma (SDH) with unilateral hemisphere vascular engorgement was demonstrated on CT scan. In those cases, the cause of the brain swelling/dysautoregulation was ascribed to the presence of the acute SDH rather than to the acceleration/deceleration forces that caused the SDH. We believe that the brain swelling is due to "second-impact dysautoregulation," rather than due to the effect of the SDH on the underlying hemisphere. To support our hypothesis, we present 10 additional cases of acute hemispheric swelling in association with small SDHs in athletes who received a second head injury while still symptomatic from a previous head injury. The clinical history and the unique neuroimaging features of this entity on CT are described and illustrated in detail. The CT findings included an engorged cerebral hemisphere with initial preservation of grey-white matter differentiation, and abnormal mass effect and midline shift that appeared disproportionately greater than the size of the SDH. In addition, the imaging similarities between our patients and those with non-accidental head trauma (shaken-baby syndrome) will be discussed.

FIG. 1.

(Case 6) Typical imaging findings of dysautoregulation/second-impact syndrome (DSIS). (A and B) Admission non-contrast axial CT images, and (C) artist's rendition demonstrate a small heterogeneous left frontal subdural hematoma (SDH; white arrows), that causes complete effacement of the basal cisterns and brainstem distortion. Note the subtle linear increased density in the region of the circle of Willis (black arrow), consistent with “pseudo-subarachnoid hemorrhage,” resulting from the marked elevation in intracranial pressure. Although there is preservation of the gray-white matter differentiation, there is asymmetric enlargement of the left hemisphere, consistent with hyperemic cerebral swelling (dysautoregulation). Note how side A is smaller than side B, even though the left hemisphere is mildly compressed by the overlying SDH. The extent of mass effect and midline shift is disproportional to the volume of the SDH (compare with Figs. 3 and 4). This 3-day-postoperative FLAIR MR image (D), and artist's rendition (E), demonstrate bilateral multifocal ischemic lesions involving several vascular territories, including the left posterior cerebral artery, thalamus, insular cortex, basal ganglia, and orbitofrontal cortex. Diffusion-weighted MR images were positive for acute ischemic injury, and the gradient-echo sequence excluded hemorrhage in these areas (not shown).

FIG. 2.

(Case 9). Typical imaging findings of dysautoregulation/second-impact syndrome (DSIS). (A) Admission non-contrast axial CT image demonstrates a small mildly heterogeneous holohemispheric left temporal subdural hematoma (SDH; arrow), with complete effacement of the perimesencephalic cisterns and convexity sulci, and severe brainstem distortion. (B) An image at the level of the centrum semiovale shows a 9-mm SDH with asymmetrical enlargement of the left hemisphere, and relative preservation of gray-white matter differentiation, consistent with hyperemic cerebral swelling (dysautoregulation). Note how side A is smaller than side B, despite the mild compression from the overlying SDH. The extent of mass effect and midline shift is disproportional to the volume of the SDH (compare with Figs. 3 and 4).

FIG. 3.

Typical acute subdural hematoma (SDH) without dysautoregulation/second-impact syndrome (DSIS) in a 17-year-old male following a motor vehicle accident (compare with Figs. 1 and 2). Admission non-contrast axial CT images at narrow (A) and wide (B) window widths demonstrate a small homogeneous left frontal SDH with minimal midline shift. Note how the volumes of the cerebral hemispheres are relatively symmetrical, and that the extent of mass effect and midline shift are proportional to the volume of the SDH.

FIG. 4.

Typical chronic subdural hematoma (SDH) without dysautoregulation/second-impact syndrome (DSIS) in a 65-year-old male (compare with Figs. 1 and 2). In contrast to DSIS patients, note how the volume of the left hemisphere (highlighted in red) is smaller than the right hemisphere. This is likely due to the absence of cerebral hyperemic swelling (i.e., intact autoregulation), combined with compression by the overlying SDH.