A unicameral bone cyst, also known as a simple bone cyst, is a cavity filled with a
yellow-colored fluid.
It is considered to be benign
Malignancy () is the tendency of a medical condition to become progressively worse.
Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malign ...
since it does not spread beyond the bone. Unicameral bone cysts can be classified into two categories: active and latent. An active cyst is adjacent to the epiphyseal plate
The epiphyseal plate (or epiphysial plate, physis, or growth plate) is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, wi ...
and tends to grow until it fills the entire diaphysis
The diaphysis is the main or midsection (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat).
It is a middle tubular part composed of compact bone which surrounds a central marrow cavit ...
, the shaft, of the bone; depending on the invasiveness of the cyst, it can cause a pathological fracture or even destroy the epiphyseal plate leading to the permanent shortening of the bone.
A latent cyst is located away from the epiphyseal plate and is more likely to heal with treatment. It is typically diagnosed in under 20 year olds.[ Although unicameral bone cysts can form in any bone structure, it is predominantly found in the proximal ]humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
and proximal femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
; additionally, it affects males twice as often as females.
Signs and symptoms
Most unicameral bone cysts do not cause any symptoms and are discovered as accidental findings on radiographs or CT scans made for other reasons.[ Large lesions can cause nearby areas of bone to thin, which may result in a fracture and cause pain.]
Cause
There is not a specific theory behind the etiology of the unicameral bone cyst, however, according to many researchers and doctors, there is a commonly known theory hypothesized by Jonathan Cohen in 1970. Cohen studied interstitial fluid in six children undergoing treatment for unicameral bone cysts. He believed that the chemical composition of the fluid found in the bone cyst was similar to the chemical make-up in serum. Cohen theorized that the unicameral bone cyst occurs when interstitial fluids in cancellous bones quickly accumulate in one region from blockage.
One of the other theories is that the cysts result from a disorder of the growth plate. Another is that the cysts result from problems with circulation that are caused by a developmental anomaly in the veins of the affected bone. The role trauma plays in the development of these cysts is unknown. Some speculate that repeated trauma puts the bone at risk for developing a bone cyst. This, however, has not been proven.
Recently, some of these tumors have been found to contain cells that express the ''FUS-NFATC2
Nuclear factor of activated T-cells, cytoplasmic 2 is a protein that in humans is encoded by the ''NFATC2'' gene.
Function
This gene is a member of the nuclear factor of activated T cells (NFAT) family. The product of this gene is a DNA-bindin ...
'' or ''EWSR1-NFATC2'' fusion gene A fusion gene is a hybrid gene formed from two previously independent genes. It can occur as a result of translocation, interstitial deletion, or chromosomal inversion. Fusion genes have been found to be prevalent in all main types of human neopla ...
. (Fusion genes are formed from two previously independent genes that become united due to a chromosome translocation
In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: reciprocal-, and Robertsonian translocation. Reciprocal translo ...
, deletion of some genetic material in a chromosome, or chromosomal inversion
An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two br ...
. These two fusion genes are described in FET gene family.) A recent study reported that the neoplastic cells in these cysts expressed a ''FUS-NFATC2'' fusion gene in four and a ''EWSR1-NFATC2'' fusion gene in two of nine test cases. It is suggested that the presence of these fusion genes indicates that SEC is a true neoplasm
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
.
Diagnosis
X-rays
Unicameral bone cysts are found incidentally on X-rays. About 90 to 95% of the lesion is found in metaphysics of long bones. The cyst is centered, oblong in shape along the long axis of a long bone. Rarely, they are large and multicameral and are found in diaphysis. When fracture is present, there may be a small bone fragment migrated in the cystic fluid. This is called "fallen fragment sign" which is diagnostic of unicameral bone cyst. Besides, a bubble migrating upwards (known as "rising bubble sign") is another feature suggesting of unicameral bone cyst.
Computerized tomography (CT) Scan
CT scan shows a thin-walled lesion with pseudo septum (incomplete septum or a septum with perforations that allows communications between two chambers). CT scan is used to assess cyst wall thickness and risk of fracture.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging scans are used to identify the precise location of the cyst, to see how aggressive the disease is, and to determine the actual shape and size. The MRI uses a combination of magnets and radio-frequencies to produce various detailed, computerized images of the cyst and its surrounding body structures.
Bone scans
a nuclear imaging method to evaluate any degenerative and/or arthritic changes in the joints; to detect bone diseases and tumors; to determine the cause of bone pain or inflammation. This test is to rule out other cysts (which are quite unusual)
Treatment
If there is a high probability of a fracture resulting from the unicameral bone cyst, then surgical treatment is necessary. Specific methods can be determined by the physician based upon the patient’s age, medical history, tolerance for certain medical procedures or medicine, health, and extremity of the disease. The treatment can involve or incorporate one or more of the following surgical methods, which are performed by a pediatric orthopedic surgeon:
*Curettage
Curettage ( or ), in medical procedures, is the use of a curette (French, meaning scoopMosby's Medical, Nursing & Allied Health Dictionary, Fourth Edition, Mosby-Year Book 1994, p. 422) to remove tissue by scraping or scooping.
Curettages are ...
:
:Surgeons create an incision or opening in the bone to drain out the fluids inside the cyst. After the fluid is drained, a curette is used to scrape the lining tissue out of the lesion.
*Bone Grafting
Bone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures that are extremely complex, pose a significant health risk to the patient, or fail to heal properly. Some small or acute fractures can be cured wit ...
:
:Bone grafting is proceeded with after curettage; the empty cavity is transplanted with donor bone tissue, bone chips taken from another bone, or artificial material.
*Steroid injection:
:An injection of methylprednisolone acetate
Methylprednisolone acetate, sold under the brand names Depo-Medrol among others, is a synthetic glucocorticoid corticosteroid and a corticosteroid ester—specifically the C21 acetate ester of methylprednisolone—which is used in clinical and ...
into the lesion helps reduce the levels of prostaglandin. Prostaglandin is a fatty acid that reduces cyst’s ability to be reabsorbed into the bone. To begin an operation using steroids, biopsy needles are placed into the cyst and the interstitial fluids are drained. The cyst is then filled with radiographic contrast to determine the volume and shape of the cyst. If the cyst can be filled, it will be injected with methylprednisolone acetate in several intervals for a time span of six to twelve months. Once the level of prostaglandin decreases, the cyst will be reabsorbed into the bone and disappear. Treatments using steroid injections are preferred over curettage, but there are few risks from the method, which are limited to infection, fracture, and reappearance of the cyst.
If a patient needs to be treated with surgery, a standard surgical procedure would be called for; the patient would be resting in Fowler’s position, a semi-sitting position, under general anesthesia. The exact size, shape, and distance between the acromion
In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acro ...
to the midpoint of the cyst are measured by a digital radiograph or MRI scan. A small, longitudinal skin incision, about 1 cm long, is made at the center of the cyst. Next, by using a trephine
A trephine (; from Greek ''trypanon'', meaning an instrument for boring). is a surgical instrument with a cylindrical blade. It can be of one of several dimensions and designs depending on what it is meant to be used for. They may be specially d ...
or drill bit, a small aperture is made inside the incision. Fluids contained in the cyst are drained and curved, metal impactors are used to break any septa
The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five coun ...
, or membranes, within the cyst. Curettes are then used to remove the entire cyst from the diaphysis. After the removal of the cystic membrane, a 95% ethanol solution is injected into the cavity to produce a chemical cauterization to burn away any residual active membrane for 30 seconds and then aspirated. Saline solution is then immediately injected into the cavity to wash out any residual ethanol solution and to mitigate any damage to healthy tissue; this irrigation process of ethanol and saline solutions is repeated for another 2 to 3 times. A curved impactor is inserted into the cavity and used to penetrate the boundary between the cyst and bone marrow; the intentional penetrations will allow bone marrow cells to migrate into the cavity to produce a source of osteoinductive cells, cells that induce bony growth. Furthermore, the cavity is completely filled with bone graft substitute, such as calcium sulfate. Finally, one cannula
A cannula (; Latin meaning 'little reed'; plural or ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces ...
ted screw is placed into the aperture.
References
External links
{{Osteochondropathy
Musculoskeletal disorders