Cranial Expansion in an Infant with Malignant Osteopetrosis (2010)

Sir: We report the first known experience with cranioplasty in the setting of untreated malignant osteopetrosis. Malignant osteopetrosis is a rare congenital disorder (one in 300,000 live births) arising from total osteoclast dysfunction that manifests in infancy as exuberant overgrowth of immature bone.1 Its only effective treatment is bone marrow transplantation, which must be performed in childhood before bony overgrowth leads to medullary obliteration with hematopoietic collapse and death.2 In our case, a 9-month-old Antiguan boy had escaped diagnosis in his own country and presented to our emergency room with advanced sequelae of untreated malignant osteopetrosis. Notable findings included severe underdevelopment (less than the second percentile growth for age), near complete medullary obliteration of the long bones with superimposed rickets arising in the setting of prolonged hypocalcemia, premature closure of the sagittal and coronal sutures with acroscaphocephaly and prominent exorbitism, hypochromic anemia with thrombocytopenia, and acquired ocular blindness presumably related to optic foraminal stenosis in the setting of his generalized bony hypertrophy. Genetic testing confirmed a principal underlying critical defect in the osteoclast lineage. Two prior reports describe successful cranioplasty following reversal of congenital malignant osteopetrosis by way of curative bone marrow transplantation.3,4 In our case, we were unable to postpone cranioplasty because investigative intracranial pressure monitoring disclosed hypertension up to 50 mmHg shortly after admission. Operative coronal exposure revealed unusual calvarial tissue that was dark crimson in color, textured like dense foam, firm but imprintable with instruments, and diffusely hemorrhagic (Fig. 1). Small eruptions of normal-appearing bone were present in each parietal zone.Fig. 1.: Elevation of the subperiosteal scalp flap revealed abnormal-appearing, diffusely hemorrhagic osteoid tissue. Note small eruptions of normal-appearing calvarial bone at the temporal apices.Hemostasis was impossible using conventional measures and case abortion was considered until it was discovered that the bleeding crimson tissue could be simply degloved to reveal a relatively normal underlying lamella of mineralized bone. This underlying layer was attenuated and internally copper-beaten but could be osteotomized and rigidly fixated in typical fashion (Fig. 2). Histologic analysis later revealed the excised tissue to be consistent with a thick rind of nonmineralized woven bone marked by exuberant extramedullary hematopoiesis.Fig. 2.: After degloving of the outer lamina of immature osteoid, the underlying bony calvaria could be expanded and rigidly fixated according to routine following osteoid removal.Despite operative débridement of a relatively large percentage of this child's residual hematopoietic tissue, we observed no significant postoperative complications such as excessive bleeding or infection. His postoperative course was relatively unremarkable and he was otherwise metabolically stabilized on temporizing calcium supplementation. In the absence of any other emergent issues, he was discharged back to Antigua at postoperative month 3 for enrollment in local bone marrow registries aimed at curative treatment of his malignant osteopetrosis. In summary, this is the first report of calvarial expansion in the setting of untreated malignant osteopetrosis. Operative intervention was notable for a thick spongy rind of immature osteoid material overlying a thin, copper-beaten bony calvaria. Operative degloving of the osteoid is described and advocated for hemorrhage control and rigid fixation of the underlying bony vault. Effective expansion was shown to be possible and postoperative healing unremarkable despite ongoing osteoclastic dysfunction and despite significant debulking of this hematopoietic material. Jon A. Mathy, M.D. Department of Plastic and Oral Surgery Mark R. Proctor, M.D. Department of Neurosurgery Gary F. Rogers, M.D., J.D., M.B.A., M.P.H. Department of Plastic and Oral Surgery Children's Hospital Boston, and Harvard Medical School Boston, Mass. DISCLOSURE The authors have no disclosures or sources of funding to acknowledge.