Miscellaneous Bone, Joint, and Soft Tissue Disorders

11 Miscellaneous Bone, Joint, and Soft Tissue Disorders

11.1 Paget’s Disease

Pathology. The etiology of Paget’s disease (synonym: osteitis deformans) is still unknown. Although a viral infection is commonly cited as its cause, this theory has remained unproven.

Paget’s disease is characterized by excessive and pathological bone remodeling, with active and inactive phases. A distinction is made between three characteristic overlapping stages of the disease that form a continuous spectrum: It starts with the lytic phase, followed by the “mixed” lytic and blastic phase, which ends in the sclerotic phase.

Clinical presentation. The prevalence of Paget’s disease varies worldwide but is generally recognized to be decreasing. The United Kingdom has the highest prevalence (4.6% of the general population). The disorder is also common in Australia, New Zealand, Western Europe, and the United States. The prevalence of the disorder increases with age.

Twenty percent of all patients with Paget’s disease are initially asymptomatic. In these patients the disease is often discovered as an incidental finding from a radiograph requested for diagnostic clarification of other signs and symptoms. However, the disease can also become clinically apparent when musculoskeletal, neuromuscular, and cardiovascular complications develop. Laboratory results reveal increased activity of serum alkaline phosphatase (sign of new bone formation) and elevated urine hydroxyproline levels (sign of bone resorption).

Location. Paget’s disease is a disease of the axial skeleton, although any bone may be involved. The skull is the most common site. The asymmetric polyostotic type (65–90% of all cases) is more common than the monostotic type.

Radiography. A conventional radiograph usually suffices to establish the diagnosis of Paget’s disease. The radiographic changes of the disease depend on the duration and stage of the disorder.

• Lytic phase. The disorder manifests in the long tubular bones as a well-defined, V-shaped area of osteolysis with a blade-of-grass or candle-flame appearance, starting at an articular surface and extending into the diaphysis ( Fig. 11.1). In the tibia, however, the osteolysis can start in the diaphysis without involving the epiphysis or metaphysis. A typical finding in the skull consists of large, well defined, oval-shaped areas of radiolucency without marginal sclerosis that cross the suture lines (“osteoporosis circumscripta”; Fig. 11.2).

• Mixed phase. This phase is characterized by a coarsening and thickening of the trabeculae and cortex ( Fig. 11.3). The trabecular thickening is found particularly along the lines of stress (e.g., thickening of the iliopectineal line; Fig. 11.4). The bones are sometimes enlarged (e.g., the ischium, pubic bone or vertebrae; see Fig. 11.4). Thickening of the cortical bone of the vertebrae may also be evident in the spine, resulting in a picture-frame vertebral body ( Fig. 11.5).

• Osteosclerotic phase. Sclerotic areas develop as a result of new bone formation ( Fig. 11.6). In the skull, this abnormal bone deposition can appear as a cotton-wool pattern. Marked thickening and sclerosis of the diploic space combined with basilar invagination is known as a “Tam o’ Shanter skull” (named for a traditional Scottish cap) ( Fig. 11.7). “Ivory vertebrae” can develop in the spine ( Fig. 11.8).

Fig. 11.1 Typical appearance of Paget’s disease in the osteolytic phase. Blade-of-grass or candle-flame appearance of osteolysis showing contact with the joint.

Fig. 11.2 Osteoporosis circumscripta of the skull in Paget’s disease.

Fig. 11.3 Typical appearance of Paget’s disease in the mixed phase. (a) Trabecular thickening (arrow). (b) Thickening of the cortical bone (arrow).

Fig. 11.4 Typical appearance of pelvic involvement in Paget’s disease during the mixed phase.

Fig. 11.5 Typical demonstration of Paget’s disease with a “picture-frame” vertebral body at L1.

Fig. 11.6 Paget’s disease of the first metatarsal in the sclerotic phase.

Fig. 11.7 Typical image of the skull in Paget’s disease. (a) Radiograph showing a cotton-wool appearance of the skull. (b) Expansion and sclerosis of the diploic space.

Fig. 11.8 Diffuse sclerosis (ivory vertebra) of C2 in a patient with Paget’s disease.

CT. The same diagnostic criteria as for conventional radiographs apply and are displayed unobscured by overlying structures ( Fig. 11.9).

MRI. Although enlargement of the bone and cortical or trabecular thickening are recognizable on MRI, these findings are better seen on conventional radiographs. The involved bone maintains the signal intensity of fat within its bone marrow ( Fig. 11.10). Mild heterogeneity of the bone marrow is still normal. Marked heterogeneity or extensive loss of signal should be an alert for a complication (e.g., pathologic fracture or tumor). Increased bone perfusion results in characteristic contrast enhancement.

NUC MED. An unusually marked increased uptake in all three phases with some expansion of the bone is characteristic on the bone scan ( Fig. 11.11). However, the bone scan can also be normal in some cases of metabolically inactive Paget’s disease.

Complications of Paget’s disease. The complications of Paget’s disease can be divided into nonneoplastic and neoplastic complications.

• Nonneoplastic complications:

Osseous weakening: This can result in bowing of the long tubular bones ( Fig. 11.12) and basilar impression.

Insufficiency fractures (see Fig. 11.12).

Pagetic arthropathy: The hip and the knee joints are particularly affected ( Fig. 11.13).

Neurologic complications: These can develop as a result of spinal stenosis, stenosis of the neural-exit foramina or cranial nerve compression.

• Neoplastic complications: Pagetic sarcoma develops in 1% of all patients. Histologically this may be an osteosarcoma, a pleomorphic sarcoma, or uncommonly a chondrosarcoma ( Fig. 11.14).

Caution

Not every tumor in Paget’s disease is a pagetic sarcoma; metastatic spread from other tumors is statistically more common.

DD. In the majority of cases a characteristic radiograph allows the unequivocal diagnosis of Paget’s disease.

Metastases. Bony alterations in Paget’s disease are better demarcated; cortical bone destruction and soft tissue swelling are not typical. Unlike sclerotic metastases, Paget’s disease involving the spine results in thickening of the cortex as well as osseous expansion and often involves the neural arches and spinous processes.

Fibrous dysplasia. Fibrous dysplasia usually affects the outer calvarial table, whereas Paget’s disease demonstrates involvement of both the outer and inner tables.

11.2 Sarcoidosis

Sarcoidosis is a systemic, granulomatous, inflammatory condition of unknown origin. Musculoskeletal involvement in sarcoidosis is rare and usually clinically asymptomatic.

Skeletal sarcoidosis classically affects the phalanges of the hands and feet, rarely the long tubular bones and the axial skeleton. Acute arthropathy tends to be self-limiting and commonly associated with erythema nodosum and bilateral hilar lymphadenopathy (Löfgren syndrome). As a rule, sarcoid arthropathy affects the ankle joint, the knee, the wrist, and the proximal interphalangeal joints.

Radiography/CT. Skeletal sarcoidosis classically presents as coarse reticular or lacelike honeycomb alterations of the trabeculae in the phalanges of the hands and feet. Cystic lesions are also commonly evident in the phalanges with punched-out cortical erosions. Bone destruction can result in acro-osteolysis, pathologic fractures, and deformity of the phalanges ( Figs. 11.15 and 11.16). Periostitis is characteristically absent and the adjacent joints are usually not affected. Involvement of the soft tissue results in destruction of the cortex from without.

In sarcoidosis, involvement of the joints often exhibits no alterations on the radiograph or merely osteopenia and soft tissue swelling.

Fig. 11.9 Paget’s disease of the lumbar spine. (a) Increase in AP diameter of L3 with concomitant loss of height. (b) Thickening of the cortex and particularly the cancellous trabeculae.

Fig. 11.10 MRI of the radius in a patient with Paget’s disease. Note the largely preserved fatty marrow! Same patient as in Fig. 11.1.

Fig. 11.11 Markedly increased bone metabolism in the right femur of a case of monostotic Paget’s disease. Bone scan (late phase).

Fig. 11.12 Tibial involvement in Paget’s disease. (a) Typical anterior bowing (sabre shin). (b) The magnified image shows a concomitant insufficiency fracture.

Fig. 11.13 Marked osteoarthritis with acetabular protrusion of the left hip in a patient with Paget’s disease.

Fig. 11.14 Sarcoma of the right humerus in a patient with Paget’s disease.

Fig. 11.15 Sarcoidosis of the phalanges. (a) Honeycomb-like alterations and soft tissue swelling of the middle phalanx of the middle finger. Involvement of the soft tissue results in destruction of the cortex from without. (b) Over time there is progression with acro-osteolysis and involvement of the index finger.

MRI. MRI of skeletal sarcoidosis is nonspecific (see Fig. 11.16) and, without available clinical information, can be mistaken for bone metastases, especially in the long tubular bones and in the axial skeleton. Possible findings of muscular sarcoidosis:

• Diffuse muscle edema may be present in the acute stage.

• Nonspecific muscular atrophy may be identified in the chronic stage.

• A nodular appearance may be evident, albeit rare. The nodular type commonly develops at the musculotendinous junction. It demonstrates a fibrous, central, stellate nodule on all sequences and does not enhance with contrast. On T2W sequences this nodule has a central starshaped area of decreased signal intensity surrounded by a hyperintense area that enhances diffusely with contrast and is composed of edema and granulomas (the “dark star sign”).

11.3 Hypertrophic Osteoarthropathy

Pathology. Hypertrophic osteoarthropathy, formerly known as hypertrophic pulmonary osteoarthropathy (synonym: Pierre–Marie–Bamberger disease), was first discovered as a paraneoplastic syndrome associated with bronchial carcinoma. It is divided into a primary (rare) and a secondary form (~ 95% of cases). The primary form is also known as “pachydermoperiostosis” and represents a congenital disorder. Unlike the primary form, secondary hypertrophic osteoarthropathy is associated with a large number of neoplastic, infectious and inflammatory diseases, with bronchial carcinoma being the most common ( Table 11.1). The exact pathogenesis of hypertrophic osteoarthropathy is still unclear, although it is assumed that vascular endothelial growth factor plays a decisive role. Hypertrophic osteoarthropathy occurs almost exclusively bilaterally and always in the tubular bones, with the tibia and fibula being most commonly affected ( Fig. 11.17).

Note

An established diagnosis of (secondary) hypertrophic osteoarthropathy of unknown origin should prompt further diagnostic examinations, especially in search of a tumorous disease (most commonly: bronchial carcinoma).

Clinical presentation. Painful swellings in the diaphyseal region of the long tubular bones and clubbing of the fingers are the cardinal symptoms.

Radiography/CT. Bilateral and symmetrical, periosteal new bone formations of the tubular bones are characteristic. They appear primarily in the diaphysis and progress toward the metaphysis ( Fig. 11.18; see also Fig. 11.17). Periosteal new bone formation progressing into the epiphysis would suggest a diagnosis of primary hypertrophic osteoarthropathy. The morphology of periosteal new bone formation (lamellated, onion-skin type, solid) can be most varied and depends on the duration of the illness.

MRI. MRI demonstrates the nonspecific signs of periostitis.

NUC MED. A bone scan is very sensitive; increased tracer uptake precedes radiographic findings ( Fig. 11.19).

DD. Chronic venous insufficiency. It is possible to differentiate periosteal new bone formation secondary to chronic venous insufficiency from hypertrophic osteoarthropathy by their different clinical presentations.

Thyroid acropachy. This characteristically affects the hands and feet, sparing the long tubular bones.

11.4 Melorheostosis

Pathology. Melorheostosis is a rare, nonhereditary, benign mesodermal dysplasia. It primarily involves the long tubular bones and their adjacent soft tissues. All age groups can be affected. The etiology of the disease is unclear. Melorheostosis spreads along so-called sclerotomes (zones of the skeleton that are supplied by an individual, spinal sensory nerve).

Radiography. The finding of dense, linear, cortical hyperostosis along the longitudinal axis of the tubular bone is pathognomonic. Its configuration is more undulating, comparable with wax dripping down the side of a burning candle ( Fig. 11.20). The hyperostosis may also cross the joint and involve contiguous bone ( Fig. 11.21).

Note

The dripping candle wax sign is indeed pathognomonic of melorheostosis but not always recognizable. Sometimes an osteoma-like appearance predominates ( Fig. 11.22). Endosteal hyperostosis can also develop, resulting in partial or complete obliteration of the medullary cavity (see Fig. 11.21). Juxta-articular ossifications within the soft tissue ( Fig. 11.23)—sometimes even at a distance from the bony alterations—have also been reported.

Fig. 11.16 Sarcoidosis of the foot. (a) Honeycomblike alterations of the fifth ray with acro-osteolysis of the third toe. (b) MRI reveals complete destruction of the distal phalanx of the third toe due to a marked soft tissue component.

Fig. 11.17 Characteristic appearance of hypertrophic osteoarthropathy involving both lower legs.

Fig. 11.18 Hypertrophic osteoarthropathy involving the metacarpals and the proximal phalanges.

Fig. 11.19 Bone scan of a patient with hypertrophic osteoarthropathy. Typical uptake along both tibiae.

Fig. 11.20 Classic “dripping candle wax sign” in melorheostosis of the fibula.

Table 11.1 Causes of secondary hypertrophic osteoarthropathy

Region	Disorders
Lungs and pleura	• Bronchogenic carcinoma • Lymphoma • Abscess • Bronchiectasis • Metastases • Mesothelioma • Pleural fibroma
Gastro-intestinal tract	• Ulcerative colitis • Crohn’s disease • Liver cirrhosis • Esophageal cancer • Coeliac disease • Lymphoma • Whipple’s disease • Polyposis
Cardiovascular system	• Congenital cyanotic heart disease
Various organ systems	• Nasopharyngeal cancer • AIDS (acquired immune deficiency syndrome)

Fig. 11.21 Polyostotic melorheostosis of the radius and the hand. In part, complete obliteration of the medullary cavity.

CT/MRI. Melorheostosis tends to be an incidental finding on imaging. The findings of projection radiography also apply for CT, where they are unobscured by overlying structures ( Fig. 11.24). On MRI, loss of signal predominates on all sequences. Soft tissue involvement appears on CT as soft tissue density and ossifications within the soft tissue that are characteristically not connected with the adjacent bone ( Fig. 11.25). Unlike CT, the appearance of soft tissue involvement on MRI is most varied and depends on the degree of mineralization.

DD. Parosteal osteosarcoma. This has an irregular pattern, is not as homogeneously dense, and results in bone destruction.

Osteopathia striata. This benign dysplasia of bone involves the medullary cavity of the tubular bones and is usually bilateral. The findings are of epiphyseal and metaphyseal location and appear as more streaked and pillarlike striations. They are vertically orientated (“celery stalk metaphysis”).

Note

Osteoma, osteopoikilosis (cf. Chapter 4.3.1), osteopathia striata, and melorheostosis are all mesodermal, benign dysplasias. Demarcation between these pathological conditions is sometimes difficult but clinically not particularly relevant.

11.5 Calcifications and Ossifications of the Soft Tissues

11.5.1 Soft Tissue Calcifications

Soft tissue calcifications may be classified according to location (generalized or localized) or on the basis of their causes:

• Soft tissue calcifications due to disturbances of calcium phosphate metabolism.

• Soft tissue calcifications with normal calcium phosphate metabolism.

• Soft tissue calcifications in dystrophic or necrotic tissue.

A special group comprises the joint-related soft tissue calcifications (hydroxyapatite deposition disease, calcium pyrophosphate deposition disease [CPPD], gout), which are dealt with in detail in Chapter 10.9.

Soft tissue calcifications due to disturbances of calcium phosphate metabolism. The most common causes of soft tissue calcifications secondary to disturbed calcium phosphate metabolism (synonym: metastatic calcification) are renal osteodystrophy and hyperparathyroidism; less common causes are listed in Table 11.2. All forms are found, ranging from fine, stippled to coarse calcifications. Hyper-parathyroidism demonstrates a predominantly periarticular distribution.

Soft tissue calcifications with normal calcium phosphate metabolism. The most common cause of this form of soft tissue calcification, which is also synonymously known as “idiopathic calcinosis,” is collagenosis. A variant is “pseudotumorous” (also: tumoral) calcinosis. It usually occurs in the 20th to 40th years of life (males are more commonly affected than females) and is associated with extensive calcifications, especially in the region of major joints. The radiographic appearance of calcifications is that of a conglomeration of many calcified nodules, ranging in size from 1 to 20 cm, which are demarcated from each other by fine radiolucent lines (see Fig. 11.27).

Dystrophic calcification. Dystrophic calcification is caused by any form of tissue necrosis, the most important being burns and frostbite. Additional causes are listed in Table 11.2. See also Fig. 11.28.

Radiography/CT. The radiographic appearance of soft tissue calcifications is characterized by stippled, circumferential, extensive densities. The patterns appearing on radiographs and CT do not always allow differentiation of the cause of the calcification. In the first instance, however, distribution pattern and laboratory results are indicative.