History and Pathogenesis

Howship was the first to report a patient with a growing skull fracture.¹ In 1816, he described a 9-month-old child in whom an enlarging defect in his parietal bone developed after an injury. The defect was apparent within 2 weeks after the injury and never resolved. The boy was re-examined when he was 4 years old and “the opening in the cranium remained undiminished. Upon laying the hand on the part, the pulsations of the brain were felt strong and distinct.”

The first account of the pathology of this condition was by Rokitansky in 1856.² He reported a 5-month-old who struck his head during a seizure and subsequently an enlarging scalp mass developed. Therapeutic puncture of the mass was performed, after which meningitis developed and the child died. At autopsy a large bone defect was found along with an associated dural tear and injury to the underlying brain.

Sporadic accounts of similar cases were published over the ensuing 50 years. Although the pathogenesis of growing fractures remained obscure, there was clear understanding of the salient clinical features of these lesions. As Godlee wrote in 1885,³

Acting on this knowledge, the first repair of a growing fracture was performed by Sir Charles Balance in 1907.⁴

Subsequently, a great deal has been written about growing skull fractures, much of which deals, either directly or indirectly, with defining the pathogenesis of the condition. Essentially all authors have recognized that a dural laceration is necessary for the development of an enlarging defect. There has been disagreement about the relative importance of leptomeningeal and parenchymal injury, the microscopic anatomy of the site, and the motive force that causes expansion of the fracture.

Dyke introduced the term leptomeningeal cyst in 1937.⁵ In an article that dealt primarily with the radiographic characteristics of these lesions, he suggested that after a fracture with an associated dural tear, “loculated, fluid-filled spaces form cysts and, owing to the pulsations of the brain, the overlying bone is absorbed.” Pathologic data confirming this hypothesis were not presented. A similar idea was offered by Taveras and Ransohoff in 1953.⁶ They reviewed their experience with seven patients whom they had operated on over a 20-year period. All seven had broad dural lacerations with cystic lesions underlying their cranial defects. The authors thought that these cysts were caused by cerebrospinal fluid that became trapped in a herniated section of arachnoid membrane and enlarged because of a ball-valve mechanism. Presumably, the cysts prevented bone reapproximation and, because of their increasing size and the pulsations of the underlying brain, led to bone resorption.

Other observations have failed to confirm the central role of leptomeningeal cysts in the pathogenesis of growing fractures. As part of a larger discussion of skull defects, Penfield and Erickson described a patient with an enlarging defect at the site of a childhood fracture.⁷ At surgery, brain, but no cyst was found in the defect. Tenner and Stein also described herniated brain within the ossification defects in children with growing fractures and highlighted the importance of local brain injury and swelling in their development.⁸ Additionally, these authors made the point that porencephalic cysts can be seen in the parenchyma adjacent to the fracture site. This comment predicts the results of Roy and colleagues, who looked more specifically at the microscopic anatomy of growing fractures.⁹ They operated on 17 patients and presented detailed histopathologic findings from the group. They found that the brain was abnormal in every case with areas of gliosis often admixed with focal areas of necrosis and what seemed to be a combination of old and new damage. Cystic degeneration was common. The authors concluded “… that leptomeningeal cyst formation, emphasized by some workers, does not take place or is extremely rare. Cysts, observed in such cases, generally result from absorption of necrotic brain followed by gliosis. …”

Rosenthal and associates helped clarify the type of injury that is necessary to cause a growing fracture.¹⁰ They performed craniotomies in 28 puppies and found that both the dura and arachnoid had to be opened to produce an enlarging fracture and that concomitant injury to the brain did not increase the likelihood that a growing fracture would develop. Clinical confirmation of the finding that dural/arachnoidal laceration, without brain injury, is sufficient to cause an enlarging fracture came from a study by Winston and coworkers.¹¹ They described four patients in whom growing fractures developed after craniosynostosis repair. In only one of the children had a dural laceration been recognized at the time of the first operation; none had any reported parenchymal injuries. At repair, all four were found to have broad dural defects with brain tissue herniating through them. Interestingly, seizures developed in two of the four children, and one of the two with seizures became hemiparetic more than a year after the first operation. The authors thought it likely that these problems were secondary to injuries caused by progressive herniation of the brain through the dural defect.

This concept of delayed or secondary injury is of importance in patients with growing fractures. Although many of the children described have had significant neurological deficits from the time of their injury, there are several reports of progressive dysfunction that develops months or years after the event.^11–15 This has been attributed to brain injury caused by (1) local brain herniation and consequent ischemia, (2) repetitive trauma to the exposed brain on the bone edge or by direct concussion, and (3) physical distortion of the brain related to its displacement.⁹ Winston and coauthors’ report offers important evidence that such injury can, in fact, occur even in the absence of significant preexisting brain damage. Given histologic descriptions of ongoing injury to both the bone and brain in this group of patients, there is strong reason to believe that secondary injury is a clinically significant problem.