35.1 Introduction

Fibro-osseous lesions of the jaws and craniofacial skeleton occur quite commonly in childhood and adolescence and represent a varied group of bone and connective tissue proliferative processes that result in an aberrant proliferation of a mineralized product and collagen. Fibrous dysplasia, ossifying fibroma, and osteoma are the three classic entities of this group of bony tumors. They are distinguished from each other by different clinical, radiological, and histological characteristics that help arrive at a diagnosis. Although often not readily apparent, accurate diagnosis is imperative, since each entity has different indications for intervention. Surgery is the mainstay of treatment for these lesions once an intervention is indicated, usually due to functional or esthetic impairment caused by the lesion growth. The course of treatment should be planned and individualized based on the manifestations, the type and location of the lesion, the natural history of the disease, and the age of the patient.

35.2 Patient Evaluation

A complete history is an essential part of the preoperative evaluation, and it should include a timeline of lesion growth or any dynamic changes, as well as careful assessment of any symptoms. Some symptoms may not be readily apparent, since most of these lesions tend to grow slowly. The most common clinical presentation for fibro-osseous lesions is facial swelling and asymmetry. Other signs and symptoms include headache, nasal obstruction, visual disturbances, and neurological changes. These lesions are, however, often asymptomatic, and they are discovered incidentally when imaging is performed for other reasons.

Physical examination should consist of a complete head-and-neck examination, including a flexible endoscopy, and a careful cranial nerve function assessment. Further evaluation depends on the location of the lesion, and may require a multi-disciplinary assessment. Lesions involving the temporal bone require an audiometric evaluation. A dentist or a maxillofacial surgeon should be part of the treating team when the mandible or maxilla is involved. Lesions involving the orbital bone or the sphenoid bone require a full ophthalmologic evaluation, including best corrected visual acuity, visual field, color vision, and examination of the fundus, all for the early detection of the most subtle changes. Participation of a neurosurgeon in treatment planning and surgery is indicated when the lesion involves the skull base.

For radiographic evaluation, a computerized tomographic (CT) scan is the most appropriate imaging modality for bony lesions. The CT scan may also be used for the intraoperative image-guided navigation system, but it may expose the child to a considerable amount of radiation, especially if repeated periodically. Magnetic resonance imaging (MRI) is useful for avoiding radiation, and also has the benefits of characterizing soft tissue and demonstrating the relation of the lesion to vital structures. Specific features characteristic of each lesion will be discussed separately. Three-dimensional (3D) craniofacial analysis and virtual surgical simulation have been recently integrated into the craniofacial surgery armamentarium, offering the surgeon a more precise surgical and reconstruction planning. ¹

A biopsy may be obtained if the involved site is amenable to biopsy. However, in some cases, obtaining a biopsy may not be possible or necessary. Fibro-osseous lesions consist of a diverse group of conditions with similar histological appearances. Thus, a definitive diagnosis usually cannot be made by histological examination alone, and both clinical and radiological correlations are needed. The surgeon must bear in mind that these lesions may be vascular and tend to bleed, and therefore be prepared for such an eventuality.

35.3 Fibrous Dysplasia

Fibrous dysplasia (FD) is a non-neoplastic bone disease characterized by intramedullary accumulation of fibrous tissue and immature woven bone. It may affect a single bone (monostotic) or multiple bones (polyostotic) throughout the skeleton. Monostotic FD accounts for approximately 80% of cases, of which 10% to 20% occur in the head and neck. Polyostotic FD tends to occur at an earlier age than monostotic FD. It accounts for approximately 20% of cases, and involves the craniofacial bones in about 50% of them, although it can approach 100% in severe cases. ² When limited to the head and neck and present within several contiguous bones, (e.g., the maxilla, zygoma, frontonasal, and temporal bones) it is termed craniofacial fibrous dysplasia (CFD) and does not constitute a polyostotic disease. ³ Polyostotic FD can be associated with McCune–Albright syndrome, which is also characterized by hyperfunctional endocrinopathies (e.g., precocious puberty, hyperthyroidism, Cushing syndrome, and acromegaly) and cutaneous hyperpigmentation (café au-lait), and usually presents in females. ^{4 , 5}

The maxilla and the mandible are the most common sites of FD lesions in the craniofacial bones, followed by the sphenoid, ethmoid, frontal, and temporal bones. Onset is usually during periods of rapid bone growth, typically presenting in teen and adolescent years, although severe forms can arise in infancy. In most cases of CFD, the presenting symptoms are slow-growing painless swelling and craniofacial deformity (▶ Fig. 35.1). Other symptoms include facial pain and headache, nasal obstruction and sinusitis, facial numbness, pathological fractures, orbital dystopia, diplopia, proptosis, blindness, epiphora, facial paralysis, loss of hearing, and tinnitus. At the same time, these lesions are often asymptomatic and discovered incidentally when imaging is performed for other reasons. Infrequently, young children and pre-pubertal adolescents may present with an abrupt alteration in the clinical course of the lesion, manifested by rapid growth, cortical bone expansion, and displacement of adjacent structures, resulting in functional deficits. In some patients, this acute change in growth behavior can be associated with secondary pathologies, such as mucoceles, aneurysmal bone cysts, or more rarely with malignant transformation. Malignant transformation, typically into a sarcomatous lesion, is estimated to occur in 0.5% of monostotic FD cases and in 4% of McCune–Albright syndrome cases. ⁶ Currently, there are no biomarkers to predict the behavior of these lesions, and their histology does not provide reliable prognostic or predictive information.

35.4 Imaging

CT imaging without contrast is the recommended modality for defining the anatomy of individual lesions and for establishing the extent of disease. The most common radiographic characteristic of CFD is a “ground-glass” appearance together with a thin cortex and without distinct borders (▶ Fig. 35.2). While different patterns may be observed, with some being mostly sclerotic and some being predominantly cystic or lytic, there is most often a combination of both patterns. This variation of the radiographic appearance of CFD depends on the age of the patient. In pre-pubertal patients, lesions most often appear homogeneous and radiodense. As these patients enter the second decade of life, the lesions progress to a mixed radiodense/radiolucent appearance that stabilizes in adulthood. This natural progression of FD should be differentiated from the development of a secondary disorder (e.g., aneurysmal bone cyst, malignant transformation), which is associated with an abrupt change in the course of development.

MRI may be used for monitoring growth, thus avoiding the exposure of children to ionizing radiation as a result of repeated CT imaging. MRI is also accurate in analyzing the spatial relationship of the lesion with critical neurovascular structures.

Radionuclide bone scintigraphy may be considered at the initial presentation if polyostotic disease is suggested by the clinical course. Increased tissue uptake is nonspecific, and lesions cannot be distinguished from malignancy.

35.5 Management of Fibrous Dysplasia

The clinical and biological behavior and the progression of FD are variable and unpredictable, thereby making the management of this condition difficult with limited published evidence and only few established clinical guidelines. Thus, appropriate treatment for FD is often highly individualized and based on patient-specific presentation. Treatment planning must take into account several factors, including the location of the lesion and its relationship with critical anatomic structures, the lesion’s clinical behavior, the nature of symptoms, the assessed potential for reactivation or regrowth, and the patient’s age and preferences. Treatment options fall into one of three categories: expectant management, medical treatment, and surgery. Surgery is the mainstay of treatment in FD, with the primary goals of symptom relief, functional restoration or preservation, and esthetic optimization. However, the timing, technique, and, in some instances, indications remain controversial.

It is generally acceptable that small, often incidentally diagnosed lesions that do not seem to progress or cause significant functional or esthetic impairment may be managed with a “watch and wait” approach, which should include periodic clinical and radiographic assessments to evaluate disease progression and obviate potential complications. A more vigilant follow-up by a multidisciplinary team is indicated in asymptomatic patients in whom the lesions involve the orbit, optic canal, skull base, or temporal bone, and it should consist of periodic ophthalmologic, neurologic, or audiometric evaluations, respectively.

No medical treatment is currently available to cure or definitively halt the progression of FD. In recent years, medical therapy with bisphosphonates has been implemented in an attempt to control pain and stabilize the lesions; however, long-term effects are controversial. There has been mixed success in reducing pain and slowing the rate of growth in CFD. Medical management has had a greater role in non-craniofacial FD, in which fractures and chronic pain are more common. Given the increased risk of bisphosphonate-related osteonecrosis, the undetermined efficacy of bisphosphonates in the management of CFD, and the unknown long-term effects of bisphosphonate treatment in children, further studies are necessary before these medications can be recommended.

Radiotherapy must be avoided, since it is ineffective and increases the incidence of malignant transformation 400-fold. ⁷

Surgical intervention is advocated once the lesion becomes aggressive or symptomatic, causing functional deficits, such as sinus obstruction, visual disturbances, intracranial complications, and cranial nerve palsies. However, indications and timing for surgical intervention are less clear when the patient presents with a solely esthetic alteration not associated with functional symptoms, especially in children. The surgical treatment of CFD can be broadly categorized into two different approaches. One is the conservative approach, which consists of debulking and contouring of the dysplastic bone tissue and often requires repeat surgery over time. The other is the radical approach, which consists of complete removal of the pathological bone tissue and its reconstruction with an autologous bone graft. In the past, conservative contouring of bone was the preferred treatment for CFD; however, the reported regrowth rates for this approach were up to 25 to 50%. ^{7 , 8} Advances in surgical techniques have enabled more radical surgery and immediate reconstruction with good aesthetic and functional outcomes, as well as with significantly lower recurrence rates. Nevertheless, in pediatric patients, each case must be carefully evaluated, and when surgery is indicated, the surgical treatment plan should be as conservative as possible, with the morbidity of the intervention being weighed against its potential benefits.

Only a few treatment algorithms for CFD have been published, and clear and well-established treatment guidelines are still lacking, especially for pediatric patients. In 1990, Chen and Noordhoff ⁹ divided the craniofacial skeleton into four anatomic zones, and proposed a surgical approach for each zone, based on esthetic, functional, and surgical considerations, thus providing some practical general principles for surgical management of CFD. Zone 1 represents the fronto-orbital, zygomatic, and upper maxillary regions; zone 2 corresponds to the hair-bearing cranium; zone 3 refers to the central cranial base, petrous, mastoid, pterygoid, and sphenoid bones, where major vessels and nerves can be encased by the lesion; and zone 4 comprises the teeth-bearing portions of the skull, the maxilla and mandible. Those authors recommended radical resection and reconstruction for lesions in zone 1, conservative remodeling and bone recontouring for lesions in zones 2 and 4, and surgical treatment only in the presence of symptoms in zone 3. This classification continues to be valid; however, it does not specify special considerations for the management of CFD in children. Additional detailed CFD management guidelines were more recently proposed, based on anatomical sites, clinical behavior, and symptoms, and they also included special considerations for application in the pediatric population. ^{10 – 13}

The following are the recommendations for the management and the surgical approach in pediatric CFD, based on the site of involvement. In general, we advocate conservative management in prepubescent patients, and deferral of surgical intervention until after puberty whenever possible. A key principle of our surgical approach in CFD, particularly in children, is to ensure that no greater deformity or functional loss is incurred than that sustained by the lesion itself.

35.5.1 Facial Bones

The most frequent presentation of CFD is a painless facial swelling and asymmetry with no associated functional symptoms. In these cases of a stable non-aggressive lesion that causes facial deformity, the question when to operate arises. Surgical treatment for esthetic indications is usually postponed until after puberty when the patient is skeletally mature and the lesion growth subsides, since interventions at a younger age may require revision surgery sooner. This disadvantage is partially offset by the benefits of early intervention in patients for whom the cosmetic deformity is intolerable. Thus, counseling for patients and their caregivers is imperative, and information regarding the probable regrowth of the lesion requiring further surgery must be provided. The patient and caregivers should also know that there is always some risk of regrowth, even when conservative surgery is performed after puberty, especially in polyostotic disease. ^{13 , 14} If surgical intervention is opted for in such cases, conservative surgical remodeling is usually preferred over radical resection with reconstruction, thus enabling esthetical and functional improvements with a less complex surgical intervention and avoiding disruption of craniofacial growth centers.

Surgical intervention in the short term is more clearly indicated for patients with an aggressive and rapidly expanding lesion. Associated symptoms may include new-onset pain or paresthesia, diplopia, proptosis, epiphora, nasal congestion, or malocclusion. Lesions that exhibit aggressive behavior are usually associated with excessive hormonal drive in the setting of underlying endocrinopathy, or, alternatively, with a secondary disorder developing within the primary lesion that includes associated expansile lesions, such as an aneurysmal bone cyst or a mucocele, malignant transformation, or osteomyelitis. The etiology of this change in behavior should be evaluated promptly by a multidisciplinary team and the patient should undergo imaging studies, tissue biopsy, and growth hormone excess assessment prior to surgical intervention. Untreated endocrinopathies should be managed aggressively. In cases of aggressive, rapidly growing lesions, it seems that the best therapeutic option is radical surgical resection with contemporary reconstruction, since it is generally agreed that radical resection is curative with minimal recurrence (▶ Fig. 35.3). Nevertheless, treatment plans for pediatric patients should be individually tailored, and the surgical approach should be determined based on the size and location of the lesion, the anticipated residual defect, and the underlying etiology. Large resections may inflict significant morbidity and disrupt craniofacial growth centers, resulting in significant functional and cosmetic deficits and facial asymmetry. Furthermore, free flap reconstruction in children, which is often required following large resections of facial bone lesions, is more complicated than in adults, and involves special functional and cosmetic concerns, such as donor-site morbidity, differential craniofacial growth, and the anticipated growth of anastomosed vessels. ¹⁵ Thus, despite higher rates of recurrence with contouring procedures, repeated debulking may be associated with less morbidity than a single major surgical procedure. We distinguish between two scenarios. One is when the residual defect is anticipated to be large, in which case conservative debulking and bone remodeling should be considered as the first choice in pediatric patients, thereby delaying the performance of a more aggressive surgical intervention until after puberty. The other is when the lesion and the anticipated residual defect are small, in which case radical resection may be considered, followed by reconstruction using local flaps or bone grafts, such as autogenous rib graft for mandibular reconstruction. These latter cases may require further surgical intervention with free flap reconstruction once skeletal maturity has been reached.

In cases of aggressive behavior due to secondary disorder, the treatment is dictated by the diagnosis. Aneurysmal bone cysts may be managed with curettage of the lesion and contouring of the underlying FD. Malignant transformation, typically into a sarcomatous lesion, requires en bloc resection with adequate oncological margins.

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