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Osteomyelitis

Summary

Osteomyelitis is an infection of medullary bone that results in the progressive inflammatory destruction of bone and the apposition of new bone. Hematogenous osteomyelitis occurs most commonly in the distal femur, proximal tibia, proximal femur and proximal humerus.

Most commonly occurs in young children. When presented in adults, patients most commonly diagnosed are elderly or IV users.
In children Hematogenous spread of infection presents as a high fever, malaise, local pain and swelling.In adults, the clinical presentation may be deceptive, since fever, elevated white count, and history of a possible source of infection are often lacking.
The lesion may appear quite aggressive by tumor criteria. Bone scan has poor specificity. Use of radiographic images is more helpful in diagnosing children than it is with adults.
Complete Information on this Tumor
Introduction and Definition: 

Osteomyelitis is an infection of medullary bone that results in the progressive inflammatory destruction of bone and the apposition of new bone. Pus spreads in vascular channels, increases intraosseus pressure and causes a decrease in blood flow. Ischemic necrosis follows and the devascularized bone is known as sequestra.

Osteomyelitis may be caused by direct inoculation secondary to trauma or surgery. Osteomyelitis secondary to trauma is often poly-microbial. Osteomyelitis can also be the result of contiguous spread from an abscess or sinus tract. Chronic osteomyelitis may occur secondary to syphilis and can cause bony destruction known as a gumma.

Incidence and Demographics: 
Hematogenous osteomyelitis occurs most commonly in the distal femur, proximal tibia, proximal femur and proximal humerus, all areas of rapid growth and trauma. The occurrence of osteomyelitis is more common in children than adults. In children, Hematogenous infection spread happens easily. However, in adults hematogenous osteomyelitis is rare except IV drug users and the elderly.
Symptoms and Presentation: 

In children Hematogenous spread of infection presents as a high fever, malaise, local pain and swelling. The clinical picture may be equivocal, and the concern about the possibility of a tumor may arise. The most common organism in patients over the age of three is coagulase positive staph aureus.In adults, the clinical presentation can be quite deceptive, since fever, elevated white count, and history of a possible source of infection are often lacking. IV drug users often have unusual organisms such as pseudomonas. Older patients may have gram negative bacteria in the spine secondary to organisms that originate as a urinary tract infection and travel through Batson's plexus. Spinal osteomyelitis may present as back pain with negative blood cultures.

X-Ray Appearance and Advanced Imaging Findings: 
The lesion may appear quite aggressive by tumor criteria. Bone scan has poor specificity. CT scan or MRI may show edema, medullary destruction, periosteal reaction, soft tissue mass or damage or articular involvement. On MRI scan, T1 weighted images demonstrate infection as a low signal with ill defined margins. T2 images show infection as a bright signal. MRI shows marrow replaced by edema and inflammatory cells but is not useful if hardware is present. In children, plain radiographs show a central lytic defect with surrounding sclerosis, termed a Brodie's abcess. In adults,the relatively aggressive radiographic appearance of the lesion may give rise to concern about a primary or metastatic bone tumor. Suspected osteomyelitis may not be positive on plain x-ray initially. Later, a mixed lytic and sclerotic lesion is seen, which has a wide zone of transition and a variable amount of periosteal reaction.
Histopathology findings: 
Microscopic examination reveals micro-organisms, neutrophils, congested or thrombosed blood vessels, and necrotic bone. Sequestra has no living osteoblasts within lacunae.
Treatment Options for this Tumor: 
Treatment for osteomyelitis is difficult. Surgical sampling or needle biopsy is necessary for diagnosis. Infected hardware should be removed if the bone is healed and stable. Acute osteomyelitis is treated with irrigation and debridement as necessary, followed by four to six weeks of antibiotics. Chronic osteomyelitis is best treated with thorough debridement, antibiotics, and local flap coverage if necessary. Complete immobilization maybe necessary to protect the vascular channels necessary to promote healing.
Outcomes of Treatment and Prognosis: 
Squamous cell carcinoma is a known complication of chronic long term draining fistula sites due to osteomyelitis.
Suggested Reading and Reference: 
References Lew, DP and FA Waldvogel, Osteomyelitis, New England Journal of Medicine, 336(14):999-1007, April 3, 1997. Deely, DM and ME Schweitzer, MR Imaging of Bone Marrow Disorders, Radiologic Clinics of North America, 35(1):193-211, January, 1997. Bullough, Peter, Orthopedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997. Huvos, Andrew. Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.
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