BENIGN AND MALIGNANT OSTEOGENIC TUMORS OF BONE
- Osteomas and exostoses are usually of no consequence unless they occlude a sinus or create a cosmetic or functional problem or are multiple and possibly syndromic.
- Osteomas and osteochondromas can mimic masses of some other origin.
- Bone origin lesions are usually better evaluated with computed tomography, and magnetic resonance imaging is used adjunctively when necessary.
- Pathology of bone lesions should almost always be read together with the imaging findings to produce the best diagnoses and optimize medical decision making.
Tumors of bone may come from one of several cell lines, and more than one line of differentiation may be present in any particular benign or malignant bone tumor. Those arising from the osteocyte that may be encountered in the head and neck are discussed here. Fibro-osseous, dental-origin, chondroid, and osteoid tumors and tumors arising from osteoclasts, metastases, and bone cysts are discussed separately in Chapters 39–42 and 99.
Clinical Perspective and Pathology
Osteomas are benign growths of mature bone.1–3 The nature of the osteoid matrix is described in more detail in Chapter 12. In the head and neck region, osteomas involve the skull, facial bones, and neck and clavicle (Figs. 38.1–38.3). Most are inconsequential. They may be properly differentiated clinically from tori and reactive bone changes, such as the cold water–induced exostoses of the external auditory canal and others, or just lumped with those same common processes involving mature bone proliferation (Fig. 38.2). Importantly, some present as masses that would be more ominous, and imaging can drastically alter the diagnostic and therapeutic process (Fig. 38.3).
Occasionally, osteomas produce symptoms that will be correctable with surgery. This is often the case in obstructing osteomas in the sinuses and external auditory canal (Figs. 38.1 and 38.3). Most often, they require no therapy.
Osteomas may arise in the medullary space or along the periosteum (Figs. 38.1–38.3). They may be sessile or attached to the bone of origin by a pedicle. Sinus osteomas are most common in the frontal sinus followed by the ethmoids, maxillary sinuses, and the sphenoid sinus in order of decreasing frequency (Fig. 38.3). Osteomas usually present between the ages of 15 and 40 years.3,4 Most are discovered incidentally. Multiple osteomas may be associated with Gardner syndrome.
Three types of osteoma are recognized: (a) osteoma eburneum with lamellated dense bone and haversian spaces (Fig. 38.1); (b) osteoma spongiosum composed of mature cancellous bone and, therefore, marrow spaces (Fig. 38.3A–C); and (c) osteoma durum lying somewhere in between the two just described1–5 (Fig. 38.3D,E).
Treatment is surgical. The need for surgery is based on the existing potential for complications such as sinus drainage occlusion. Sarcomatous changes do not occur in osteomas. Regrowth should not follow gross total removal.
The computed tomography (CT) and magnetic resonance (MR) morphology may vary slightly based on these subtypes (Figs. 38.1–38.3). All show a mature bone pattern on CT.5 Fatty or hematopoietic marrow may be more apparent on MR than CT. Obviously densely compact bone shows up as a signal void on MR and may go unappreciated, especially when projecting into an aerated sinus.
Clinical Perspective and Pathology
These may be either a developmental abnormality or true neoplasm. Osteochondroma can be called an osteocartilaginous exostosis. It is predominantly of osseus origin, but an osteochondroma will have a cartilage cap. It grows by enchondral ossification of this cartilage component (Figs. 38.4 and 38.5). These lesions are most common in the extremities.