Presentation of Systemic Disease When Imaging the Lower Extremity

HELENE PAVLOV

CAROLYN M. SOFKA

SATINDER S. REKHI JR.

JESSICA R. SPIVEY

The foot and ankle are constantly being stepped on and stressed by both normal and extraordinary forces. Feet are taken for granted, until they are hurt, limit ambulation, make wearing shoes difficult, cause gait disturbances, or some other malady forces the foot and/or ankle to take on a new level of importance. Most of the time, foot conditions are localized to a bunion, flat foot, or Achilles tendon injury that can be treated with orthotics, change of footwear, exercises, local injection, or a combination of these therapies and/or surgery. On other occasions, foot and/or ankle pain and abnormalities of the lower extremity may result from an underlying systemic condition. When reviewing imaging examinations, for example, radiographs (X-ray), magnetic resonance imaging (MRI), ultrasound, or computerized tomography (CT) examinations of the lower extremity, possible underlying systemic conditions must be considered. Familiarity with systemic conditions that can be identified on an imaging examination facilitates early diagnosis and intervention. These conditions fall into the classic categories of arthritis, infection, tumor, vascular, developmental, metabolic, and other. In this chapter, the imaging findings of various systemic conditions that can present with changes in the lower extremity are organized alphabetically.

Fibrous Dysplasia

Fibrous dysplasia is a sporadic bone disease in which benign fibro-osseous lesions develop during skeletal formation.¹ Occasionally, fibrous dysplasia can arise as a component of McCune-Albright syndrome or Mazabraud syndrome.² Lesions can occur anywhere on the skeleton, with the craniofacial bones, ribs, and long bones most commonly involved.¹ In the lower extremity, the femur and tibia are most often affected.¹ Fibrous dysplasia occurs in both monostotic and polyostotic forms, with the former accounting for approximately 80% of all cases.² Often asymptomatic, fibrous dysplasia is diagnosed incidentally on radiographs obtained for unrelated reasons.¹ In such cases, no treatment is needed.¹ The polyostotic form is more likely to produce symptoms including pain, limp, and deformity, and large lesions are prone to pathologic fracture.¹ Rarely, fibrous dysplasia is complicated by malignant degeneration, particularly in previously irradiated areas.¹

FIGURE 1-1. Radiographic pattern of fibrous dysplasia. Frontal X-ray of the lower extremities (A) and left femur (B) demonstrates expansile lesions with characteristic ground glass matrix, thin cortices, and bowing deformities. Not atypically, polyostotic fibrous dysplasia affects one side more than the other.

Fibrous dysplasia demonstrates a characteristic radiographic appearance of intramedullary, well-defined, and expansile lesions with a radiolucent “ground glass” matrix.¹,² Shepherd’s crook deformity of the proximal femur is a lateral bowing deformity and coxa vara.² Saber shin deformity is an anterior bowing deformity of the tibia commonly associated with fibrous dysplasia (Fig. 1-1).

Gout

Gout, an inflammatory arthritis, is a crystal arthropathy characterized by hyperuricemia and subsequent deposition of monosodium urate (MSU) crystals in joints and soft tissues.³ Gout is a common and potentially debilitating condition, disproportionately affecting men.³ Affected individuals experience recurrent acute inflammatory flares as well as chronic
destructive changes secondary to MSU crystal deposition. Gout can involve any joint but most frequently affects the feet, demonstrating a predilection for the 1st metatarsophalangeal (MTP) joint.⁴ Gout can be associated with metabolic syndromes, myocardial infarction, and diabetes mellitus.

Radiographs of involved joints may reveal marginal “punched out” erosions, sclerotic margins, and overhanging edges, with relative preservation of the joint space; however, X-ray changes typically occur late in the course of the disease.³,⁴ Radiographs may also demonstrate macroscopic depositions of MSU crystals, or tophi, which are a hallmark feature of chronic gout.⁴ Tophi may be periarticular or intra-articular; CT is particularly useful in detecting intra-articular depositions.⁴ Tophi display intermediate or low signal on T1-weighted MRI sequences, with variable appearance on T2-weighted sequences.³ Postcontrast sequences generally demonstrate enhancement, and there is often associated synovial thickening and adjacent marrow edema.³,⁴ MRI can also reveal erosions before they become visible on radiographs (Fig. 1-2).⁴

FIGURE 1-2. Radiographic and MR patterns of gout. A and B: Frontal and oblique radiographs of the foot in different patients with gout. A: Frontal X-ray of the foot demonstrates medial soft tissue prominence of gouty tophus adjacent to the metatarsal head of the great toe without underlying bone or joint abnormalities. B: Oblique X-ray view demonstrates classic “overhanging edge” of gout at the medial and lateral aspects of the metatarsal head of the great toe. C to E: MR demonstration of gout. C: Coronal fast spin echo MR image of the 1st MTP joint demonstrates the heterogeneously hyperintense soft tissue mass of gouty tophus medial to the 1st MTP joint. D: Coronal fast spin echo proton density-weighted image demonstrates a heterogeneous expansile hyperintense mass of gouty typhus circumferentially about the 3rd PIP joint. E: Axial fast spin echo proton density-weighted image through the forefoot demonstrates focal heterogeneously hyperintense soft tissue tophus within the plantar margins of both the 1st and 3rd MTP joints. The soft tissue tophus about the 3rd MTP joint extends dorsally.

Hypertrophic Pulmonary Osteoarthropathy

Hypertrophic pulmonary osteoarthropathy (HPO) or Pierre Marie-Bamberger syndrome is a syndrome of unknown etiology characterized by the triad of periosteal bone deposition, clubbing of the digits, and arthralgia, which occurs in association with pulmonary pathology.⁵,⁶ HPO can develop in many chronic pulmonary conditions, but in the majority of cases is associated with primary lung malignancies.⁵ Rarely, patients with extrathoracic diseases such as inflammatory bowel disease can develop HPO.⁵ Patients typically present with pain, tenderness, and swelling. Radiographs demonstrate generalized periosteal reaction along the diaphyses and metaphyses of long bones sparing the epiphyses.⁶ MRI can be helpful in demonstrating adjacent soft tissue swelling and muscular edema (Fig. 1-3).⁶

Infarct And Osteonecrosis

Osteonecrosis and bone infarct define bone death. Osteonecrosis is typically used to describe ischemic bone death in a subchondral location, and bone infarct is used when the lesion is not in a subchondral location. Systemic causes of bone death are corticosteroids, sickle cell anemia, collagen vascular disease, alcoholism, and idiopathic.⁷ The most common cause of osteonecrosis in a subchondral location is trauma that presents as mixed lytic and sclerotic areas on radiographs and that can progress to microfractures in articular collapse if left untreated.⁸

FIGURE 1-3. Radiographic presentation of HPO. A: X-ray of the right ankle demonstrates thick periosteal reaction at the distal aspect of the long bone, sparing the epiphysis (arrow) without underlying bone pathology. Posteroanterior (PA) radiograph of the chest (B) in the same patient demonstrates a large, left upper lobe lesion.

Infarcts in the lower extremity occur primarily in the medullary cavity of the long bones.⁸ On radiographs, infarcts present as an elongated serpiginous rim of sclerosis with a central lucency. MRI is the most sensitive test for suspected bone infarct and demonstrates characteristic findings.⁷ The lesions contain a center of devitalized marrow surrounded by a rim of granulation tissue and sclerosis, which gives these lesions a central high signal from adipose marrow with a surrounding ring of hyperintense inner granulation tissue and hypointense outer ring of sclerosis and is classically referred to as the “double-line” sign (Fig. 1-4).

Maffucci Syndrome

Maffucci syndrome is a nonhereditary and rare dyschondroplasia of unknown origin characterized by multiple enchondromas combined with soft tissue venous malformations.⁹ Enchondromas are benign cartilaginous lesions within the metadiaphysis of tubular bones that typically present as osteolytic expansile lesions with central stippled calcifications characteristic of a chondroid matrix (Fig. 1-5).¹⁰

Melorheostosis

Melorheostosis is an uncommon sclerosing bone dysplasia of unknown etiology.¹¹,¹² Patients are usually asymptomatic but can present with limb stiffness or pain.¹¹ The typical appearance on radiographs is of flowing hyperostosis along the outer cortical surface of the long bones of the lower extremity, which usually has an undulating appearance, referred to as “dripping candle wax sign” (Fig. 1-6).¹¹

FIGURE 1-4. X-ray and MR findings of bone infarct. A: Lateral X-ray of the ankle demonstrates a classic bone infarct with an irregular serpiginous elongated lucency in the distal tibia without periosteal or endosteal reaction (arrow). Sagittal inversion recovery (B) and proton density-weighted images (C) demonstrate the characteristic heterogeneously hyperintense serpiginous pattern of bone infarct on MRI.

Metastatic Disease

Bone is a common site of metastatic involvement in malignancy.¹³ Many primary malignancies can metastasize to the skeleton; however, breast, prostate, and lung carcinoma are most frequently associated with osseous involvement.¹³ Less frequently, kidney and thyroid cancers metastasize to the bone. Metastatic lesions can be painful and may lead to pathologic fracture if extensive cortical destruction is present.¹⁴ The axial skeleton and proximal long bones are disproportionately affected in metastatic disease, in part because of the higher relative content of vascularized red marrow.¹⁴

The radiographic appearance of osseous metastases depends on the primary malignancy and the bone response elicited by the metastatic deposit.¹³ Breast and lung carcinoma typically produce mixed lytic and blastic lesions.¹³ Lytic lesions are characterized by excessive bone resorption and are often seen with thyroid and renal carcinoma, whereas blastic (sclerotic) lesions, characterized by excessive bone formation, are often seen with prostate carcinoma.¹³ Radiographic features associated with osseous metastases include poorly defined margins, endosteal scalloping, cortical destruction, and periosteal reaction. An extraosseous soft tissue component may occasionally be associated (Fig. 1-7).¹⁴

FIGURE 1-5. Radiographic manifestations of Maffucci syndrome in two separate patients. A: Standing anteroposterior (AP) examination of the lower extremities demonstrates numerous deforming enchondromas throughout the right lower extremity involving the tibia, fibula, femur, and the pelvis. Asymmetric distribution is common, with up to 50% of lesions being unilateral.⁹ B: Lateral view of the right tibia and fibula demonstrates soft tissue calcifications representative of venous malformation anterior to the knee and tibia. C: AP of the foot demonstrates classic calcified venous malformations in the soft tissues and scalloping of the metatarsals. The enchondromas are less evident in the foot of this patient.

FIGURE 1-6. Radiographic and CT presentation of melorheostosis. AP (A) and lateral (B) X-rays of the left knee demonstrate the classic “dripping candle wax” appearance of melorheostosis with cortical hyperostosis along the posteromedial aspect of the distal femur and the medial cortex of the tibia. Small extraosseous soft tissue ossification in the posterior muscle is seen on the lateral radiograph. C: Frontal radiograph of the left ankle in the same patient demonstrates a large ossification in the soft tissues inferior to the medial malleolus, representing an uncommon extraosseous manifestation of melorheostosis. D: Coronal reformatted CT image of the left hip demonstrates a heterogeneous ossific mass contiguous with the lesser trochanter in this patient with melorheostosis.

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