Further characterization of traumatic subdural collections of infancy

Abstract

Bilateral convexity and interhemispheric subdural hematomas are common neuroimaging patterns seen in infants who have sustained nonaccidental head injuries (NAHIs). These collections often appear aschronic or acute-on-chronic on computerized tomography (CT) studies. To determine the nature of these extraaxial fluid collections and their relationship to cerebrospinal fluid (CSF) dynamics, the authors studied five infants with suspected NAHI in whom symptomatic bilateral mixed- or low-density subdural collections were revealed on imaging studies; the patients underwent burr hole evacuation of the hematoma and external drainage. Once decompression was achieved, radiotracer was injected into the lumbar subarachnoid space, and the subdural drainage system was monitored for appearance of the isotope. In all five cases, the radiotracer moved rapidly from the lumbar subarachnoid space into the convexity subdural space and then into the external drainage system. This indicated the possibility that some of these mixed-density subdural collections were acute blood mixed with CSF rather than acute-on-chronic collections arising from rebleeding subdural membranes. The authors propose that, during infancy, tears in the loosely adherent arachnoid envelope at the main arachnoid granulation site along the superior sagittal sinus may result in a considerable amount of CSF mixing with acute blood in the subdural space, creating a hematohygroma.

Prevalence of Subdural Collections in Children with Macrocrania

“…17 12,14,16 "Subdural hematoma" has been used very loosely in the literature in this population and probably has described a wide range of SDC with different etiologies, including "subdural hygroma," 25 "chronic subdural hematoma," 16 "chronic subdural hematoma with rebleeding," 12 and "hemato-hygroma." 14 In clinical practice, it is often difficult to differentiate these, adding to the complexity in evaluating these children. 12,25 For this reason, we chose to use the nonetiologic term "subdural collections" in our study to describe these collections.…”

“…However, some theories have been postulated. 12,14 Enlargement of the subarachnoid space may stretch and place increased strain on bridging veins, with resultant rupture and SDH formation. 7,13,29 This potential increased strain on bridging veins has been modeled mathematically 13 but is not universally accepted.…”

“…6 Some investigators have suggested that children with macrocrania and enlargement of the SS may be at increased risk for subdural hemorrhage (SDH) after minimal or no trauma. [7][8][9][10][11][12][13][14][15] A clinical dilemma often arises when subdural collections (SDC) are identified in children with enlarged SS because the identification of SDC in an infant without an appropriate traumatic history raises the concern for abusive head trauma (AHT). 3,12,16,17 The literature connecting enlarged SS and risk of SDC is based predominately on case reports or small case series.…”

Serial neuroimaging in infants with abusive head trauma: timing abusive injuries

“…31 Several authors have hypothesized that mixed-density SDH may reflect an admixture of fresh clotted blood, unclotted blood or serum, and/or CSF from the subarachnoid space that has migrated into the subdural space through a tear in the arachnoid membrane. 9,11,33,39 A communication between the subarachnoid and subdural spaces in infants with SDH was confirmed in one study by injecting a radioisotope into the CSF via lumbar puncture at the time of subdural drain placement and identifying the radioisotope within the subdural fluid within 3-24 hours. 39 It is apparent that although mixed-density SDHs are more common after AHT, and some of these likely represent acute and prior injuries, the fact that they are also present early after presumably single accidental injuries makes their interpretation more difficult.…”

“…Homogeneously hyperdense SDH was present in fewer than one-third of our cases; mixed-density SDH, containing both hyperdense and hypodense components, was present in over half of the infants in the present study, in onethird of children in our prior study, 9 and in 91% of infants with AHT in a third study by Vinchon et al 31 Mixeddensity SDH in AHT has been interpreted as prima facie evidence of serial injuries, 6,25 but this concept has recently been challenged. 9,11,32,33,39 One child in our previous study developed a hypodense subdural collection de novo on a second CT scan performed 19 hours after an initial scan showed no SDH in that region. 9 In another study of 18 infant victims of motor vehicle crashes with SDH, 3 infants had mixed-density SDH on the initial CT scan.…”