Introduction
Fibrous dysplasia (FD) is characterized by slow, progressive replacement of a localized area of bone by an abnormal proliferation of isomorphic fibrous tissue intermixed with poorly formed, haphazardly arranged trabeculae of woven bone [
1]. In 1937, McCune and Bruch first suggested that among all of the abnormalities of bone formation, this disorder should have its own place as a distinct clinical entity [
2]. The following year, Lichtenstein introduced the term “fibrous dysplasia” [
3]. The lesion of fibrous dysplasia appears in three distinctive clinical patterns: (1) single bone involvement (monostotic form), which is the most common presentation (70 percent of patients); (2) multiple bone involvement (polyostotic form), a less common form (30 percent); (3) McCune-Albright syndrome or the rare Mazabraud syndrome [
4,
5]. The skull bone/orbit is usually involved in monostotic fibrous dysplasia [
6,
7]. Cranial bone involvement of FD usually presents as an enlarging mass with symptoms resulting from the mass effect exerted by the lesion [
6]. Expansion of the lesion and the resultant pressure may produce thinning of the overlying cortical bone, but the lesion does not invade the surrounding normal tissues [
8]. However, FD may be complicated by pathologic fracture, and rarely by malignant degeneration [
5]. Herein, we present 6 cases of FD involving the calvarium in children, and attempt to put forward a useful strategy for the diagnosis and treatment of these lesions in children along with a review of the literatures.
Patients and methods
Subjects
Six cases of FD involving the calvarium managed at the Department of Pediatric Neurosurgery of Tianjin Children’s Hospital and Department of Neurosurgery of General Hospital of Tianjin Medical University between May, 2000 and July, 2006 are reported here. All the patients had a calvarium lesion without manifestations of FD in the remainder of the body. They commonly presented with enlarging mass and cosmetic complaints (Fig. 1). There were 4 males and 2 females, with ages ranging from 5 to 12 years. Table 1 shows the age, sex, clinical symptoms, locations, surgical procedure, outcome and follow-up of these patients.
Methods
Imaging examination
All patients underwent CT screening (in which, two patients underwent three-dimensional CT scan) (Figs. 2, 3). Two patients received MRI screening of the head. FD in this series was monostotic, and involved frontal bone (2 cases), temporal bone (1 case), parietal bone (2 cases), and occipital bone (1 case). The imaging characteristics of the lesions were described as follows: Pagetoid pattern in 4 cases, sclerotic pattern in 3 cases, oval lucent region surrounded by a capsule of dense bone in 1 case (case 4). The patients in this study exhibited one or more of these patterns on the radiographic studies. Three-dimensional CT images show the extension of lesions.
Surgical methods
All the patients underwent surgical biopsy (2 cases) or excision (4 cases) for therapy and/ or diagnosis. Of the 4 patients suffering cranial resection, one underwent facial degloving and craniofacial resection for extensive orbital rim involvement, one underwent minimal shaving for cosmetic purpose, and the other 2 underwent craniotomy (of them, one was planted a titanium armor plate to repair skull after frontal craniotomy) (Fig. 4). The other 2 cases refused surgery intervention, and only underwent surgical biopsy to confirm a histopathological result.
Results
Histopathology findings
The histopathology of the lesion in the 6 cases show characteristic features of FD consisting of small, principally non-mineralized, trabeculae of woven bone in bland cellular and collagenous matrix (HE staining, × 100, × 400 ) (Fig. 5). A hemorrhagic and necrotic cystic lesion in the expanded bone was found in one section in case 4 (Fig. 6), which corresponded to the oval lucent region surrounded by a capsule of dense bone on a CT image.`
Outcomes and follow-up
The outcome of all the 4 cases taking surgical treatment was excellent. There was no surgical mortality. No recurrence was found in the patients undergoing cranial resection during the follow-up lasting 18 to 50 months. The other 2 patients did not undergo surgical intervention and as a result, their skull lesions still exist and have been managed conservatively. Of these, the course of one patient was stable (case 1), and the mass in another expanded from 1.5 cm in diameter initially to 2.2 cm at the last review (case 5).
Discussion
FD is a benign but slowly progressive bone disorder of unknown origin in which normal cancellous bone is replaced by immature woven bone and fibrous tissue. It is a relatively uncommon, non-familial congenital disorder of bone [
1,
9] that is usually manifested before the third decade of life [
10]. There is no sex preference [
9]. FD accounts for approximately 2.5% of all bone tumors and nearly 7.5% of benign bone neoplasms [
11,
12]. It may occur in its monostotic form, or involve multiple foci including the long bones, skull, and cranial base. Significantly, in 50% to 100% of patients with the polyostotic form and in 10% with the monostotic variant craniofacial involvement is present [
9]. There is a predilection for involvement of the frontal, sphenoid, ethmoid and maxillary bone complexes [
13]. Various terms have been applied to FD with craniofacial involvement, including craniomaxillofacial, cranio-orbital, frontoorbital, orbital and complex fibrous dysplasia [
11,
14].
The precise etiology of FD is currently unknown. More recent attempts to define the disorder have focused on its underlying genetics and molecular biology. Lee and his coworkers [
15] proposed that abnormal intracellular regulation of cyclic adenosine monophosphate or protein kinase A was a possible etiologic factor in the development of FD. Several other researchers [
16-
18] have identified mutations in the Gs-α gene as a cause of FD, which results in altered activity of intrinsic GTPase activity or the Gs protein signal transduction pathway. It has thus been postulated that the pattern and distribution of FD depends on which tissues contain the mutated Gs-α (GNAS
1) gene and is in turn affected by such factors as genomic imprinting. During the next several years, as the underlying molecular biology of the disorder becomes elucidated, the true etiology of fibrous dysplasia will also be found.
The radiographic characteristics of FD, as described by Fries in 1957, are pagetoid (56%), a mixture of dense and radiolucent areas of fibrosis, sclerotic mass (23%) if homogenously dense, cystic (21 %), spherical or ovoid lucency surrounded by a dense boundary [
1,
19]. CT is the workup of choice for diagnosis and follow-up because on the basis of the images of CT. Bony detail can be clearly shown and the extent of the lesion can be accurately assessed. Furthermore, CT can distinguish fibrous dysplasia from other osteodystrophies of the skull base, including oteosclerosis, osteogenesis imperfecta, Paget’s disease and osteopetrosis [
6]. CT demonstrates the classic “ground-glass” appearance of the sclerotic form and provides excellent visualization of the extent to which the disease impinges on the cranial basal foramina and other structures [
20]. Three-dimensional CT scanning also is extremely useful in delineating the lesion and guiding the surgeon when intervention is being contemplated. The cystic and mixed forms appear inhomogeneous in texture in the expanded bone on CT scans [
20]. The cystic lesion could be seen in case 4 of our series. Magnetic resonance imaging offers excellent definition of soft-tissue and ocular involvement and allows assessment of adjacent neurovascular structures. Lytic areas are suggestive of malignant degeneration, particularly when viewed to expand on repeated imaging [
20]. Thus, case 4 underwent radical resection with a mass without symptoms due to this reason. Symptoms arise due to the expansion and impingement of bone on adjacent structures. The most common symptom is swelling or deformity of the affected site. The definitive diagnosis of FD is based on multiple factors. Data accrued from clinical, radiological and histological examinations provide the basis for accurate diagnosis.
The establishment of appropriate therapy for this condition has been hindered by its relative rarity and by the paucity of quality reports in which adequate documentation, including careful imaging studies, is presented. Treatment options have included conservative management with clinical and radiological follow-up, medical management and surgical intervention. Radiotherapy in FD is unproven as an effective treatment modality. Moreover, it can significantly increase the incidence of radiation-related complications. Conservative management may be indicated if predicated on sound knowledge of a patient’s clinical status and radiological findings. Especially radiological data should be interpreted in light of clinical correlations. Surgical intervention may be indicated when perceived and unacceptable cosmetic deformity is present or significant, and acute and/or progressive nerve impairment is documented by serial examinations. The basic tenets of operative intervention include the improvement of cosmetic deformity and the preservation or improvement of neurological function.
In conclusion, FD involving the calvarium is typically a benign but slowly progressive disorder. Treatment strategies have included conservative management with clinical and radiological follow-up, medical management, and surgical intervention. Because of the benign nature of the condition, the surgery itself should be relatively conservative in children.
Higher Education Press and Springer-Verlag Berlin Heidelberg
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