Pathological conditions

Tumors and tumor-like conditions

 

Bone tumors may cause non-specific changes, but an analysis of these changes is very important for the further assessment of the patient. Soft

 

	Figure 90. Localized osteolytic destruction in distal portion of the femur and permeative destruction pattern more proximally (arrows). (Metastases from renal cell carcinoma.)
	Figure 91. Permeative destruction pattern (black arrows). Note destruction of the cortical bone medially (arrowheads) and the onion-peel periosteal reaction laterally (white arrow). (Aneurysmal bone cyst in early stage)

tissue tumors may grow to a considerable size before a clinical diagnosis is established.

Reactive patterns of bone

The reactive patterns of bone that develop in response to benign and malignant tumors may be similar, and these may simulate those of other conditions, such as inflammation, metabolic diseases, and trauma. The reactive patterns can be divided into (l) bone destruction (osteolysis),

	Figure 92. Sclerotic bone reaction around a localized region of destruction (nonossifying fibroma).
	Figure 93. Neoplastic bone with high density and irregular architecture. Also note the perpendicular periosteal reaction. (Osteosarcoma of the femur, radiograph of specimen.)
	Figure 94. Periosteal reaction as a single layer (black arrow) and onion-peel pattern (white arrow). (Osteoblastoma of ulna.)

(2) reactive bone formation (osteosclerosis), and (3) periosteal reaction (periostitis) .

Bone destruction can occur as a localized osteolytic region (Fig. 90), which is seen not only in benign tumors but also with metastatic disease. Bone destruction also can appear as numerous small cavities, l to 5 mm (Figs. 90, 91), a pattern that may be seen in more aggressive tumors. In any single tumor, different types of destruction may be present at the same time.

Bone reaction may be localized about the periphery of a tumor (Fig. 92), or it may be seen as diffuse sclerosis throughout the bone. Neoplastic bone (i.e., bone produced by the tumor itself) often has an irregular appearance (Fig. 93).

With slowly growing tumor, as well as osteomyelitis, a periosteal reaction may be seen as a thin calcified layer (Fig. 94). If the tumor grows more rapidly and with varying speeds, several such layers are superimposed on each other in an onion-peel pattern (Fig. 94). In rapidly growing aggressive tumors, a perpendicular periosteal reaction may be seen with calcified thin streaks, which may be oriented perpendicular to the surface of the bone. This last pattern of periostitis relates to elevation of the periosteal membrane due to rapid tumor growth, in growth of connective tissue and small blood vessels, and mineralization of bone (Fig. 93).

Principles for radiologic evaluation of tumor

Modern treatment of bone and soft tissue tumors is based on extremity preserving surgery in combination with radiotherapy and chemotherapy. This means that the orthopedic surgeon must remove the tumor with enough margin to avoid recurrence but at the same time leave as much normal tissue as possible to preserve maximum function of the extremity. From a radiologic point of view the factors most important to evaluate are the local aggressiveness of the tumor, the specific diagnosis, and the local tumor extension.

Local aggressiveness
Aggressiveness relates to how rapidly a tumor grows. Generally a relationship exists between the aggressiveness of a tumor and the grade of malignancy so that a fast growing destructive tumor tends to have a higher degree of malignancy than a slowly growing benign tumor. This relationship is not absolute, and individual cases often reveal exceptions. Thus, some benign tumors have an aggressive growth pattern, such as aneurysmal bone cysts, and some malignant tumors can grow very slowly over long periods with minimal amount of bone destruction.
Aggressiveness in a bone tumor is best evaluated on the conventional radiographic examination. Tumors can be categorized as having characteristics of slow, intermediate, or rapid growth.

A slowly growing tumor often causes a well-defined zone of osteolytic destruction surrounded by a sclerotic rim (Fig. 92). When present, a periosteal reaction, often occurring as a single layer, is seen.

A tumor of intermediate growth potential may cause a well-defined osteolytic region of destruction. The transition zone between the lesion and the normal bone is narrow and well defined. A sclerotic rim may or may not be present. The cortical bone may be destroyed or expanded. If there is a periosteal reaction it usually is seen as one layer or multiple layers with an onion peel-appearance (Fig. 91).

An aggressive tumor, rapidly growing, shows poorly defined destruction with a broad transition zone between it and normal bone. No sclerotic rim surrounds the tumor. The cortical bone often is destroyed with

Figure 95. Bone scintigraphy for evaluation of possible metastases. lncreased uptake is observed in an osteosarcoma in the distal end of the femur, and a metastasis is seen in the proximal portion of the humerus (arrowhead). (Same patient as in Figure 96.)

a soft tissue mass outside the bone. The periosteal reaction may have an onion-peel appearance, or perpendicular striations may be evident (Fig. 93).

The aggressiveness of a soft tissue mass cannot be evaluated radiologically. Deep soft tissue tumors (under the deep fascia) must be considered aggressive until proved otherwise.

Diagnosis
A single specific diagnosis may be difficult from a radiologic, pathologic and clinical point of view. The radiologist must consider a number of parameters in the diagnostic approach:
- The aggressiveness of the tumor
- The multiplicity of the tumor
- The localization of the tumor
- The specific radiologic pattern
- The age of the patient and associated laboratory results and other clinical findings

A newly recognized tumor may be solitary or multiple. Multiple lesions may indicate the presence of a multicentric tumor, such as histiocytosis X, or a primary malignant tumor that already has metastasized. Bone scintigraphy (Fig. 95) may be useful as both bone and soft tissue tumors frequently cause increased uptake of the radionuclide.

Tumor localization also is important. Bone tumors can occur anywhere in the skeleton, but many tumors predominate in specific locations. Most primary bone tumors occur in the long bones, but certain types prefer flat bones, small bones, or vertebrae. Osteomas often are seen in the skull, hemangiomas in the skull and vertebral bodies, chordomas at the base of the skull and sacrum, and enchondromas in the tubular bones of the hand. Localization in an involved bone also can be of diagnostic help. In the long tubular bones, most tumors are seen at sites where the growth is most extensive (i.e., in the proximal portion of the humerus, the distal end of the femur, and the proximal end of tibia). Several exceptions exist, however. Chondroblastomas often occur in the epiphysis before the physis is closed, and giant cell tumors originate in the metaphyses and quickly extend into the epiphysis.

In many cases the patterns of bone destruction, bone reaction, and periosteal reaction are nonspecific. Certain tumor types show a specific radiologic pattern, however. Osteosarcoma often forms neoplastic bone, which is seen as irregular, dense areas within the bone or amorphous dens e masses in the soft tissues (Fig. 96). In chondromatous tumors (enchondroma and chondrosarcoma), calcifications often are seen as punctate or ringlike regions (Fig. 97).

Certain types of soft tissue tumors can be diagnosed with a high degree of certainty with CT and MRI (e. g., lipoma) (Fig. 98), but in most cases the radiologic appearance of soft tissue tumors is not specific. CT and MRI, on the other hand, contribute to the evaluation of tumor mass, providing information regarding vascularity and necrotic areas within the tumor (Fig. 99).

Local tumor extension
The local extension of a tumor must be assessed carefully preoperatively. Previously this was accomplished with several imaging methods, such as conventional radiography, scintigraphy, and angiography. The addition of CT led to an improvement in the evaluation of tumor location and extension. Today MRI is the best method to evaluate tumor location and

	Figure 96. Osteosarcoma with irregular dense neoplastic bone in the distal portion of the femur and amorphous neoplastic bone masses in the soft tissues.
	Figure 97. Chondrosarcoma with ring-shaped thin calcifications in the tibia (arrow) and a minimal endosteal destruction (arrow-heads).

the only method generally needed in addition to conventional radiography. With MRI the tumor location in bone and tumor extension into soft tissues or joints can be diagnosed (Fig. 100). Concerning soft tissue tumors, MRI can determine the position of a tumor, the structure from which it emanates, and the involvement of surrounding structures (Fig. 99).

a	Figure 98. Lipoma. a) CT, b) MRI. With both CT and MRI, the diagnosis is established without biopsy. The low attenuation of the tumor on the CT examination and the increased signal intensity in the tumor with MRI are typical.
b
a	Figure 99. Local extension and tissue characteristics of a soft tissue tumor: MRI. a and b) T1- and T2-weighted images. The localization of the tumor in relation to surrounding muscles, vessels and nerves can be evaluated. In the T2-weighted image (b) areas with high signal intensity correspond to necrosis and liquid degeneration. (Malignant fibrous histiocytoma.)
b

Differential diagnosis

The skeletal reaction to a pathologic stimulus is non-specific, and diagnostic considerations may include other pathologic conditions, such as infections and inflammatory, metabolic, traumatic, and anomalous lesions. In some cases, it may be impossible to differentiate radiologically between a malignant tumor and osteomyelitis, and other clinical findings

Figure 100. Local tumor extension: MRI. The localization of the tumor in the femur and the violation of the cortical bone with soft tissue extension (arrows) can be seen. (Osteosarcoma.)

or even an open biopsy often is required to reach a specific diagnosis.

Stress fractures have been described earlier in this chapter. When they occur unilaterally with a diffuse sclerotic reaction it may be impossible to separate this condition from a tumor on the basis of conventional radiographic findings. Clinical history, scintigraphy, and other imaging data often are required for definite diagnosis.

Ossification anomalies can simulate a tumor radiologically, but, in most cases, such anomalies occur in specific areas and in specific age groups.

 

Niels Egund, Kjell Jonsson, Holger Pettersson and Donald Resnick