Bone cyst

Definition

A bone cyst is a cavity in bone tissue resulting from disturbances in local blood circulation and activation of enzymes that destroy the organic matter of bone. In the initial stages, it is asymptomatic or accompanied by minor pain. Often, the first sign of the pathologic process is a pathologic fracture. The disease lasts about two years; during the second year, the cyst decreases in size and disappears. The diagnosis is made based on radiography. Treatment is usually conservative: immobilization, punctures, injection of drugs into the cyst cavity, and physiotherapy. If ineffective, resection followed by alloplastic reconstruction is performed.

General information

A bone cyst is a condition in which a cavity forms in bone tissue. The causes are unknown. Children and adolescents are usually affected. There are two types of cysts: solitary and aneurysmal; the former are three times more common in boys, and the latter are usually found in girls. The cyst itself does not pose a threat to the life and health of the patient, but it can cause pathological fractures and sometimes becomes the cause of the development of contracture of the nearby joint. Neurological symptoms may appear with an aneurysmal cyst in the vertebra. Orthopedic traumatologists treat bone cysts.

Pathogenesis

The formation of a bone cyst begins with an impaired blood flow to a limited area of bone. Due to a lack of oxygen and nutrients, the area begins to deteriorate, which leads to the activation of lysosomal enzymes that break down collagen, glycosaminoglycans, and other proteins. A fluid-filled cavity with high hydrostatic and osmotic pressure is formed. This, along with the large amount of enzymes in the fluid within the cyst, leads to further destruction of the surrounding bone tissue. Subsequently, the fluid pressure decreases, the enzyme activity decreases, and the cyst turns active to passive and eventually disappears, gradually replaced by new bone tissue.

Types of bone cysts

Solitary bone cyst

Boys 10-15 years old are more often affected. However, earlier development is also possible—the literature describes a case of a solitary cyst in a 2-month-old child. In adults, bone cysts are extremely rare and usually represent a residual cavity after an undiagnosed disease in childhood. Cavities occur in long tubular bones, with bone cysts of the proximal metaphysis of the femur and humerus being the most common. 

The course of the disease in the initial stages is mostly asymptomatic; sometimes, patients note slight swelling and minor unstable pain. In children younger than ten, swelling is sometimes observed, and contractures of the adjacent joint may develop. Large cysts in the proximal diaphysis of the femur may cause lameness. In contrast, lesions of the humerus may cause discomfort and unpleasant sensations during sudden movements and lifting of the arm.

The reason for seeking medical attention and the first symptom of a solitary bone cyst is often a pathologic fracture that occurs after a minor traumatic impact. Sometimes, the trauma cannot be detected at all. When examining a patient with the initial stages of the disease, local changes are not pronounced. There is no edema (the exception is edema after pathologic fracture), hyperemia is not present, a venous pattern on the skin is not expressed, and local and general hyperthermia is absent. Minor muscle atrophy may be detected.

In some cases, a painless club-shaped thickening with bone density can be detected when palpating the affected area. If the cyst reaches a significant size, the cyst wall may deflect when pressure is applied. In the absence of a fracture, active and passive movements in full support are preserved. If the integrity of the bone is compromised, the clinical picture corresponds to a fracture, but the symptoms are less pronounced than in the case of a typical traumatic injury.

To clarify the diagnosis, a radiologic study of the affected segment is performed: radiography of the femur, radiography of the humerus, etc. Based on the radiologic picture, the phase of the pathologic process is determined. In the phase of osteolysis, the image shows a structureless rarefaction of the metaphysis in contact with the growth zone. In the delimitation phase, radiographs show a cavity with a cellular pattern surrounded by a dense wall and separated from the growth zone by a section of normal bone. In the recovery phase, the radiographs show an area of bone consolidation or a small residual cavity.

Aneurysmal bone cyst

It is less common than solitary. It usually occurs in girls 10-15 years of age. It can affect the pelvic bones and vertebrae and less frequently affects the metaphyses of long tubular bones. Unlike solitary bone cysts, it usually occurs after trauma. The cavity formation is accompanied by intense pain and progressive swelling of the affected area. Examination reveals local hyperthermia and dilation of subcutaneous veins. With localization in the bones of the lower extremities, a violation of support is noted. The development of contracture of the nearby joint often accompanies the disease. With bone cysts in the vertebrae, neurological disorders occur due to compression of spinal roots.

There are two forms of aneurysmal bone cysts: central and eccentric. The same phases characterize the course of the disease as in solitary cysts. 

Bone cyst treatment

Orthopedists, traumatologists, or surgeons provide treatment in larger communities. Even if there is no fracture, relieving the limb by using crutches (for lower limb injuries) or hanging the arm on an armband (for upper limb injuries) is recommended. If the fracture is pathologic, a cast is applied for six weeks. Punctures are performed to accelerate the maturation of the tumor mass.

The contents of the cyst are removed using special needles for intraosseous anesthesia. Multiple wall perforations are then performed to relieve the pressure inside the cyst. The cavity is flushed with distilled water or saline to remove breakdown products and enzymes. Then, it is washed with a 5% aminocaproic acid solution to neutralize fibrinolysis. At the final stage, aprotinin is injected into the cavity. With a large cyst in patients over 12 years of age, triamcinolone or hydrocortisone may be administered. With active cysts, the procedure is repeated once every three weeks, with closed – once every 4-5 weeks. Usually, 6-10 punctures are required.

X-rays are regularly monitored during treatment. If conservative therapy is ineffective, there is a threat of spinal cord compression, or there is a risk of significant bone destruction, surgical treatment is indicated – marginal resection of the affected area and alloplastic repair of the resulting defect. In the active phase, when the cyst is connected to the growth zone, surgery is performed only in extreme cases since there is an increased risk of damaging the growth zone, which is fraught with lagging growth of the limb in the distant period. In addition, when the cavity is in contact with the growth zone, the risk of recurrence increases.

All these treatment option are available in 18 hospitals worldwide (https://doctor.global/results/diseases/bone-cyst). For example, Benign bone tumor removal can be done in 7 clinics across USA for an approximate price of $4,010 – 7,870(https://doctor.global/results/americas/united-states/all-cities/all-specializations/procedures/benign-bone-tumor-removal). 

Prognosis and prevention

The prognosis is usually favorable. After the reduction of the cavity, recovery occurs, and the ability to work is not limited. Long-term consequences of cysts may be due to the formation of contractures and massive destruction of bone tissue with shortening and deformation of the limb. Still, with timely, adequate treatment and compliance with the doctor’s recommendations, such an outcome is rarely observed.