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What are Cysts? What is a Simple Bone Cyst?

Tumor lesions are often incorrectly called cysts. A cyst can be defined as a cavity filled with liquid content; in a soft tissue tumor, the cyst has a capsule and liquid content.

In layman’s terms, a lipoma on the forearm is called a small cyst, but this lesion is not cystic. We can also develop hemorrhagic cysts that form in the limbs.

The term cyst is also used to define a pseudotumor lesion in the bone (the bone cyst). In this case, the lesion does not have a capsule and is defined by an area of ​​bone sclerosis, which is regularly treated by orthopedics.

Cysts can also form during joint degeneration; patients who lose cartilage protection in a certain area of ​​the joint may have a cyst in the pelvis in the form of a subchondral cyst, also less frequently called subcortical cyst. These have similar content to the synovial fluid of a serous cyst.

The simple bone cyst is a benign bone lesion that appears as an intraosseous cavity filled with protein-rich fluid. We still don’t know what causes it, but one of the theories posits that an increase in pressure in parts of the bone leads to necrosis and the accumulation of fluid.

Other names used to define bone cysts include pseudocyst, hemorrhagic cyst, progressive bone cyst, unicameral bone cyst, idiopathic bone cavity, essential cyst, traumatic bone cyst, and solitary bone cyst.


Examples of Bone Cysts

Case 1: A patient was experiencing pain in the hip. A clinical investigation revealed the presence of a cyst in the hip, characteristically determined by the high signal on T2 resonance and low signal on T1.

Case 2: After a little physical effort, the patient felt a sudden pain in their arm and heard a clicking sound. On the radiograph, we saw a cyst in the arm bone (humerus) and a small fracture trace. These lesions develop prostaglandins, which hinders bone production.

Case 3: Case of bone cyst in the knee.

Example of surgical conduct:

Surgical incision. See what a cyst is, notice its cavity doesn’t contain any liquid?

When and Where Does the Simple Bone Cyst Occur?

● 90% of cases occur in long bones
● It usually occurs in the first two decades of life
● Humerus and femur are the most common sites

What Causes a Simple Bone Cyst and Its Development?

We still don’t know why simple bone cysts occur, but medical scientists suspect the following reasons:

● Low-grade infection
● Changes in bone growth sites
● Venous obstruction
● Increased osteolysis (bone resorption by the destruction of bone tissue)
● Intramedullary hemorrhage
● Local ischemia (decrease or suspension of blood supply to the bone(s))
● Changes in calcium metabolism
● Trauma
● A combination of these factors

Aneurysmal bone cyst/Intramedullary hemorrhage: According to this theory, trauma (“would cause” a hemorrhagic cyst), insufficient to fracture the bone, can lead to an intramedullary hematoma. This can lead to clotting, aggravating and disrupting bone repair, and degenerating and causing a cystic cavity, which decreases or suspends blood supply to the affected bone.

It can present in several places, usually in the metaphysical region as a cyst in the shoulder bone, specifically the cyst in the arm bone, the humerus.

Where Is COS (Simple Cyst) Usually Noticed?

This cyst is often difficult to diagnose in general clinics or other non-orthopedic specialties. Not all medical professionals can accurately explain what a cyst is. A simple bone cyst can be caused by several problems, including:

● A wide variety of neoplastic lesions (in practice, defined as tumors)
○ Giant cell tumor
○ Aneurysmal bone cyst
○ Fibrous dysplasia
● The vast majority of cases are asymptomatic with no noticeable symptoms, making their detection difficult.


Generally, radiographs show a radiotransparent area (where there is a compartment, a vacuum). It is somewhat regular and limited by a thin cortical halo in the peripheral region.

Definitive diagnosis

Bone cysts are confirmed by the information collected in the radiographic examination.

Is There a Need for Treatment?

The weakening of the bone or its malformation, parallel to other factors, can deteriorate the patient’s clinical condition.

A specialized doctor must analyze these cases to determine if there is a need for treatment and which one is most suitable. In the vast majority of cases, a surgical approach is not necessary—only a radiographic follow-up is required.

What Does the Treatment Consist of?

Remember that we are talking about the bone cyst and not a subcortical cyst or subchondral cyst. These injuries are usually accidentally identified; they do not trigger symptoms.

When the radiograph shows signs of risk for a pathological fracture and the patient is in pain, we can consider treatment with corticosteroid infiltration or surgery to curettage (scrape) the cavity and fill it (with bone or some biomaterial).


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