Osseous tumors represent a broad range of pathologic conditions, which can be roughly categorized into fibro-osseous lesions, cartilaginous lesions, reactive bone lesions, and vascular lesions. Most of these entities are extremely rare in the craniofacial skeleton, and particularly in the orbit. As such, this chapter predominantly focuses on fibro-osseous lesions, which represent a broad continuum of diseases with similar histopathologic features. Many of these lesions are slow-growing and can present with similar clinical symptoms, including proptosis, ocular displacement, and even ocular compartment syndrome when they occur in and around the orbit.
Ossifying fibroma and fibrous dysplasia (FD) are similar entities consisting of collagen and fibroblasts that have replaced normal bone with a variable amount of mineralized matrix containing bone or cementum. As a result, radiographic features may appear similar and can complicate diagnosis. Subtle differences between radiographic features and histopathologic features lead to an accurate diagnosis. Imaging may be helpful in distinguish between these conditions and is of further value for determining the optimal surgical approach and planning the extent of surgical intervention. However, despite being histopathologically benign lesions, these tumors can also cause significant orbital complications, facial deformity, and pain. Additionally, as discussed later, fibrous dysplasia can give rise to osteosarcoma, a malignant fibro-osseous lesion.
Benign Fibro-Osseous Lesions
Osteoma
Osteomas are the most common benign tumor of the paranasal sinuses and show a predilection for men with a male-to-female ratio of 1.5–3:1. The frontal (70% to 80%) and ethmoid sinuses (20% to 25%) are most commonly involved, followed by the maxillary and sphenoid sinuses, respectively. Osteomas are most typically diagnosed between the third and fourth decade of life and are thought to have an incidence of up to 3% of the general population and are often discovered incidentally on imaging. The exact underlying etiology or pathophysiology is not well understood; however prevailing theories postulate osteomas are either developmental, form secondary to trauma, or form secondary to infection.
In general, osteomas are slow-growing solitary lesions with an average growth of 1.6 millimeter (mm) per year (range 0.44 to 6.0 mm per year). Between 4% and 10% of osteomas produce clinical symptoms, and the symptoms are typically related to the location of the tumor, size, and growth rate. When osteomas are symptomatic, headache localized to the area over the tumor is the most common presenting symptom. Other symptoms include facial pain, swelling or deformity, nasal discharge or obstruction, and sinusitis. Orbital symptoms, including epiphora, proptosis, diplopia, and visual loss, can also be observed.
The imaging modality of choice for osteomas is a thin-slice computed tomography (CT) scan, as it provides detail regarding the size, location, and concurrent sinonasal pathology. Osteomas appear as well-circumscribed, dense masses with either a homogeneous or heterogeneous appearance ( Fig. 28.1 ). Earwaker characterized multiple types of osteomas based on CT imaging, including the following:
- 1.
Uniformly sclerotic
- 2.
Target-like lesion
- 3.
Partially corticated shell with heterogeneous matrix
- 4.
Heterogeneous matrix without a well-defined shell
- 5.
Laminated pattern
Uniformly sclerotic lesions are the most common. Depending on the histologic makeup of the osteoma, it may be hyperintense on T1-weighted magnetic resonance imaging (MRI), as in the case of sclerotic lesions, or it may demonstrate a signal void on all sequences, as in the case of heterogeneous lesions. MRI can be used as an adjunct to evaluate for mucocele formation or intracranial and intraorbital involvement.
Histologically osteomas are well-circumscribed lesions characterized by a variable amount of cancellous and compact, lamellar bone with haversian systems. They can be divided into ivory and mature types.
Surgical intervention is typically reserved for symptomatic patients, for cases when the osteoma is causing obstruction of the involved sinus, or if the lesion demonstrates rapid growth. In the instance of slow-growing, asymptomatic osteomas, conservative management with intermittent radiographic follow-up is recommended. When osteomas are complicated, symptomatic, or rapidly growing, complete excision is the treatment of choice. Recurrence rates of these lesions are low with complete excision. Small osteomas are often removed en bloc with curettes, whereas others require extensive drilling.
In giant osteomas, which are characterized as lesions more than 30 mm in largest dimension or 110 g, dura or periorbita are often encountered during resection. This has led to controversy over the optimal surgical approach. Overall, osteomas of the paranasal sinuses can be resected using endoscopic approaches, external approaches, or a combination of the two. Size and location typically define the approach. Endoscopic approaches have been used in all locations within the paranasal sinuses; however, traditionally open approaches have been used more frequently for frontal sinus lesions. Historical approaches for these masses included a Lynch frontoethmoidectomy or osteoplastic flap to facilitate access, visualization, and treatment of possible complications such as cerebrospinal fluid leak. Cosmetic and functional concerns, in addition to the advent of improved endoscopes, instruments (such as high-speed endoscopic drills, the ultrasonic aspirator), and intraoperative navigation systems, have challenged the need for open approaches. Chiu et al. identified three factors that limited endoscopic resection of osteomas from the frontal sinus: location of the base of attachment, relative size of the tumor to that of the frontal recess, and location in relation to a virtual sagittal plane through the lamina papyracea. Osteomas were classified into four grades based on these characteristics, which are summarized in Table 28.1 . Endoscopic resection was recommended for grades I and II disease, and open approaches were advised for grades III and IV. However, there have been documented reports of successful endoscopic resections of osteomas with far lateral extent or intraorbital involvement.
| Grade | Base of Attachment | Location Relative to VSPLP | Anteroposterior Diameter | Recommend Approach |
|---|---|---|---|---|
| I | Posterior-inferior along frontal recess | Medial | AP diameter of lesion is < 75% AP dimension of frontal recess | Endoscopic enodonasal |
| II | Posterior-inferior along frontal recess | Medial | AP diameter of lesion is > 75% AP dimension of frontal recess | Endoscopic endonasal |
| III | Anterior or superiorly located within frontal | Lateral | External or endoscopic-assisted external | |
| IV | Tumor fills the entire frontal sinus | External or endoscopic-assisted external |
Purely endoscopic approaches have gained significant popularity in recent decades. Although familiarity of the endoscopic modified Lothrop procedure has redefined the parameters by which frontal osteomas can be resected endoscopically, a narrow anteroposterior diameter of the frontal sinus and tumors attached to the orbital roof or anterior table of the frontal sinus significantly increase the need for open or endoscopic-assisted procedures.
Osteoblastoma (Giant Osteoid Osteoma)
Osteoblastomas are rare, slow-growing benign tumors of bone that most frequently present in the long bones or vertebrae. Rarely do they occur in the paranasal sinuses. They can be locally aggressive and highly proliferative. Most often, presentation occurs between the second and fourth decades of life. Males are twice as likely to be affected. Given the proliferative nature of these lesions, patients often present with pain, swelling, and tenderness over the lesion.
On CT imaging, osteoblastomas often originate from the surface of the bone or within the medullary cavity ( Fig. 28.2 ). They are well circumscribed with central mineralization. The expansile tendencies of these lesions lead to destruction of cortical bone and presentation of periostitis radiographically. MRI findings are nonspecific and can overestimate the size and extent of the lesion. On T1- and T2-weighted imaging, osteoblastomas appear hypointense to isointense with focal areas of decreased intensity that represent calcifications. These lesions do enhance because of their vascular nature and often demonstrate enhancement of the surrounding tissue ( Fig. 28.3 ).
Histologically these lesions are similar to osteomas; however, they contain areas of woven bone trabeculae surrounded by osteoblasts, osteoclasts, and fibrovascular stroma. As a result, osteoblastomas more frequently demonstrate rapid growth, and when the lesions involve or abut the orbit, they can cause significant symptomatic effect on the eye.
Complete surgical excision is recommended for these lesions, and both open and endoscopic approaches have been described. Recurrence rates in the paranasal sinuses are difficult to determine owing to the paucity of data. However, in other sites (e.g., spine, jaw, long bones), the recurrence rate is estimated to be between 9% and 15% up to 10 years after resection. As a result, some groups have recommended annual surveillance with CT imaging. In less than 1% of cases, osteoblastomas can transform into osteosarcoma.
Osteoclastoma (Giant Cell Tumor)
Osteoclastomas or giant cell tumors (GCTs) account for approximately 4% of primary bone tumors. Although benign, they are known for a higher rate of recurrence compared with osteomas. GCTs are most frequently noted in patients between the ages of 20 and 45. There is a slight preponderance in women. Similar to the other tumors noted in this chapter, they are more commonly found within the long bones; however, they have also been identified in the cranium. Approximately 1% of GCTs are found in the cranium, where they occur most frequently in the sphenoid and temporal bones. The clinical presentation usually involves headache and dysfunction of either cranial nerve II or VIII, depending on the location of the mass.
Diagnosis of GCTs based on imaging is difficult given the lack of identifiable radiologic features. Radiographically GCTs appear as an expansive, sometimes lytic mass that may extend to other sinuses, dura, or other nearby soft tissues. Given the nonspecific radiographic features, tissue is necessary to confirm the diagnosis.
On histology, GCTs are characterized by stromal mononuclear cells and giant cells. The mononuclear cells represent the neoplastic component of the tumor, whereas the giant cells are multinucleated and have an osteoclast-like morphology. Multiple cytogenetic abnormalities have been described, with telomeric association the most frequent chromosomal aberration (75%). These features separate GCTs from other osseous lesions in which multinucleated giant cells are observed, including giant cell reparative granuloma, FD, and aneurysmal bone cyst.
As with osteoblastomas, complete surgical resection is recommended for GCTs, as recurrence rates are high with partial resection. However, given the propensity for these tumors to develop in the sphenoid and temporal bones, aggressive surgery for complete excision must be weighed against the potential morbidity to nearby vital structures.
Ossifying Fibroma
Ossifying fibromas (OFs) are benign fibro-osseous neoplasms that involve the craniofacial bones. These tumors are divided into three variants including cement-ossifying fibroma (COF), juvenile psammomatoid ossifying fibroma (JPOF), and juvenile trabecular ossifying fibroma (JTOF). As the names imply, JPOF and JTOF are seen in juvenile patients. These tumors can be found in a fairly broad age range with some notable differences between the subtypes. JPOF and JTOF are less common than COF and typically present in the second decade of life without a gender predilection. In contrast, COF is typically seen in the third to fourth decade of life and shows a 5:1 female predilection. JPOF most commonly involves the ethmoid sinuses. In contrast, JTOF is more commonly seen in the maxilla followed by the mandible. COF occurs in the mandible most frequently, specifically in the molar and premolar regions.
Swelling is a common presenting symptom of these lesions when the maxilla and mandible are involved. Other presenting symptoms are often secondary to localized mass effect based on the location of the lesion and can include sinusitis, nasal obstruction, rhinorrhea, proptosis, diplopia, ptosis, and restriction of extraocular movements. Sinonasal OFs are considered locally aggressive and may extend into adjacent structures, including the orbit, palate, optic canal, and anterior cranial fossa. However, the lesion is bordered by a shell of bone with intact periosteum and dura mater, and thus meningitis, pneumocephalus, and neurologic deficits are rare. Blindness is rare, although it has been reported.
Radiographically OFs are initially predominately radiolucent and, as the tumor enlarges, begin to demonstrate a mixed density appearance. A thin, radiolucent band surrounds the tumor and separates it from neighboring bone. Concentric expansion of the cortical plates in keeping with a benign lesion is typically observed, and in the case of COF, the outer cortices usually remain intact ( Fig. 28.4 ). In contrast, the juvenile variants often show dehiscence along the expanded outer cortices ( Fig. 28.5 ). On MRI, these lesions show variable intensity on T1-weighted images and enhancement of fibrous portions after administration of contrast ( Fig. 28.6 ).
The histologic appearance depends on the specific variant. COFs demonstrate a variably hypercellular fibrous tissue with mineralized tissue that varies among tumors or even within the same tumor. Mineralized tissue can consist of trabeculae of bone or osteoid with a woven and lamellar pattern or as lobulated collections of cementum-like material. Another histologic feature of COFs is osteoblastic rimming. Typically mitotic figures are not observed. In JTOF, however, mitotic figures can be seen within a cellular stroma with a mineralized component consisting of a cellular osteoid trabeculae focally mineralized at the center. Osteoclastic giant cells can be seen and osteoblastic rimming is not present. JPOF demonstrates numerous psammomatoid bodies that can coalesce to form large areas of mineralization. On gross examination, the tumor appears white to yellow and is gritty in consistency ( Figs. 28.7 and 28.8 ).
The treatment of choice for sinonasal OFs has typically consisted of radical resection because of the aggressive growth behavior and close proximity to both the orbit and the skull base. A multidisciplinary approach with experts in radiology, neurosurgery, otolaryngology, ophthalmology, or craniofacial surgery may be required for optimal treatment planning. At present, radical resection is most frequently recommended to reduce the risk of local recurrence.
For many years, open surgical approaches were recommended to provide visualization of the entire lesion. Such approaches included lateral rhinotomy, sublabial approach, and craniofacial resection. However, external approaches were prone to scarring and undesirable cosmetic outcomes, as well as overresection of bone, which further placed young patients at risk for significant facial deformity. As a result, endoscopic approaches have largely replaced open approaches in an attempt to reduce scarring while achieving adequate resection. Endoscopic approaches have the advantages of direct visualization, absence of external incisions, and reduced postoperative morbidity and length of stay. However, reports of endoscopic resection have noted significant bleeding intraoperatively as a result of removing the lesion in a piecemeal fashion. These tumors are highly vascular, and with the juvenile forms are not well encapsulated, and unlike COFs, these tumors do not easily shell out. As a result, precautions, including patient positioning, optimal anesthetic, hemostatic agents, and electrocautery, should be taken to reduce intraoperative bleeding. Blood products should be readily available. Embolization of feeder vessels or ligation of branches of the external carotid artery has been reported and may be considered before surgery in some cases.
Even with complete surgical excision, recurrence rates have been reported as high as 30% to 56%. However, not all sinonasal OFs demonstrate recurrence even after a subtotal resection. Particularly in adults, there may be a role for watchful waiting with interval radiology. Radiation therapy is contraindicated because of concern for malignant transformation.
Lesions are most likely to recur in pediatric patients. Adjuvant systemic therapy with interferon-alfa has been explored for treatment of patients with juvenile ossifying fibroma to decrease the rate of local recurrence. In one case series, subcutaneous injections of interferon-alfa for 6 to 12 months were shown to prevent recurrence during a mean follow-up of 35 months in three patients. Other chemotherapeutic agents, including cyclophosphamide, samarium, and pazopanib, have been used to try to halt progression, with mixed results.
Fibrous Dysplasia
Fibrous dysplasia (FD) is another fibro-osseous tumor characterized by slowly progressive proliferation. Unlike ossifying fibroma, FD may be monostotic (involving a single bone) or polyostotic (involving multiple bones). The majority of cases are monostotic (75%). FD is caused by missense mutations in the GNAS gene whose downstream effects result in changes in bone osteoprogenitor cells, leading to abnormal bone formation.
FD is typically diagnosed in the first or second decade of life and does not show a gender predilection. Craniofacial bones and specifically the maxilla and mandible are some of the most common sites affected. The orbital roof is often involved owing to involvement of the frontal, ethmoid, or sphenoid bones. FD lesions are typically unilateral. Polyostotic FD is associated with several syndromes including McCune-Albright syndrome.
Growth of FD generally slows upon completion of skeletal growth, but the disease can progress during times of hormonal change, such as pregnancy or hormone therapy. The most common presentation is painless swelling over the involved area. This can progress to significant cosmetic deformities and, in rare cases, can affect nearby vital structures. Blindness secondary to FD has been reported.
The radiographic appearance of FD on CT is often characterized by a ground-glass quality of the trabecular bone ( Fig. 28.9 ). Other descriptions include an “orange peel” or “cotton wool” appearance because of the mixed density of the lesion. Given the expansile features of the lesion, the normal morphology of nearby structures is maintained, albeit displaced. The ground-glass appearance and lack of an identifiable margin are pathognomonic for FD. MRI can be misleading, as FD can appear more aggressive or even malignant. On T1-weighted images FD may have a low to intermediate signal intensity depending on the lesion’s makeup of fibrous and mineralized components. On T2-weighted images, the fibrous component appears hyperintense. Because of the high vascularity of these lesions, enhancement is seen on postcontrast images.
