Healing calvarial eosinophilic granuloma or healing skull fracture?

Abstract

Hollon et al. [1] report a patient with the clinical and radiographic features, characteristic for a calvarial eosinophilic granuloma (EG) or Langerhans cell histiocytosis (LCH), in whom the pathology of the lesion showed evidence of bone healing, which was interpreted as a healing skull fracture. The child was 2 years old, had a minor bump to the forehead, and 2 months later had a soft tissue mass overlying a 2.0-cm diameter skull defect, which on CT scan had irregularly eroded borders. The outer table of the skull was affected more than the inner table. The underlying brain was normal. At surgery, there was no evidence of a skull fracture beyond the limits of the known calvarial defect. Complete circumferential resection of the calvarial defect plus some associated abnormal fibrous tissue was performed. The dura was intact. The diagnosis at this stage, based on the clinical, radiographic, and intraoperative findings was solitary calvarial EG. Pathological examination showed evidence of hemosiderin laden macrophages, fibrous tissue, and reparative woven bone with osteoblastic rimming typical of bone repair. Based on these findings, the diagnosis of the pathologist was a healing skull fracture. Thus, the conclusion, based on the pathologist’s opinion, was that this was an atypical presentation of a healing skull fracture. Hence, the reason for the case report. I do not think that the authors have proven that this was a healing skull fracture. Indeed, everything except for the pathologist’s opinion indicated that this was not a skull fracture. For this to be a skull fracture with such a large cranial defect, this would have to be a form of growing skull fracture, not a simple linear skull fracture. The trauma was mild and not the type of trauma typically associated with a diastatic skull fracture, laceration of the underlying dura, or contusion of the brain, which are factors that predispose to a growing skull fracture. The outer table was involved more than the inner table, which is the opposite of what one would expect with a growing skull fracture. Furthermore, at surgery, there was no fracture line noted beyond the confines of the cranial defect to suggest that the defect was part of a skull fracture. I would suggest that there is an alternative and more probable diagnosis to explain the finding of healing bone and that is that the lesion is a healing EG of the skull. As the authors stated, all the findings, except the pathology findings pointed to EG and away from a growing skull fracture. As is typical for EG, the lesion often becomes evident after minor trauma and the CT scan findings are typical and exactly what was noted in this case. As the authors noted, there are two series of cases with spontaneous resolution of solitary calvarial EG [2, 3]. In those patients with spontaneous resolution, the scalp mass typically resolves or is much smaller by 2 months and the skull defect repairs completely over the next many months. In none of the cases reported with spontaneous resolution have biopsies been done, so we do not have information about what would be found if the healed lesion was excised prior to complete repair of the bone. However, since the bone repairs itself after the mass resolves, one would expect exactly what was found in this case, namely hemosiderin laden macrophages, fibrous tissue, and reparative woven bone with * Paul Steinbok psteinbok@cw.bc.ca