Aneurysmal bone cyst is a bone tumor-like lesion of unknown cause, which can develop alone or secondary to certain bone tumors, such as giant cell tumor of bone, non-ossifying fibroma, osteoblastoma, chondroblastoma, etc. This disease is less common.
I. Clinical characteristics
1.Age
The age of prevalence is 10-20 years old, and about 3/4 of the patients develop the disease before 20 years old, rarely after 30 years old.
2. Gender
Slightly more females than males.
3.Site
The disease occurs in the long tubular epiphysis of the extremities or the backbone, spine and iliac bone.
4.Symptoms and signs
The onset of the disease is slow, and the duration of the disease is often several months or even years, and the symptoms are local pain, swelling and different degrees of joint movement limitation. When the lesion is superficial, localized redness and swelling, vasodilation and increased skin temperature can be seen, which can be easily misdiagnosed as malignant tumor. If the lesion is located in the spine, spinal cord compression symptoms may occur. Local puncture of the lesion can produce non-coagulable dark red blood fluid with high pressure.
Imaging characteristics
1.X-ray characteristics
It can be divided into subperiosteal type and central type. The subperiosteal type is mostly located in the long bone stem and epiphysis, with eccentric, expansive, cystic osteolytic destruction, thinning and obvious expansion of the bone cortex on one side, generally with clear margins, few reactive sclerotic bands, and no periosteal reaction. In some cases, the lesion is “bubble-like”, mostly located outside the bone, surrounded by an intact or interrupted thin bone shell, with a shallow basin-like depression of the local bone cortex, but does not reach the medullary cavity, often with a soft tissue mass, which is easily misdiagnosed as a malignant tumor, and often with a large soft tissue mass when the spinal appendages are involved.
A few central lesions occur in the central part of the long bone epiphysis, which expands and expands to the periphery, and the surrounding bone cortex becomes thin and dilated in a long oval shape, which is consistent with the longitudinal axis of the bone, and there are many bony intervals within it.
2.CT and MRI
CT can clearly show the internal morphology, interval and fluid plane of the cyst, while MRI shows heterogeneous signal according to the content of liquid red blood cells in the cyst cavity, generally low signal in T1WI and high signal in T2WI.
Pathological changes
1.Major body
The surface of the lesion is covered with periosteum, and there is a thin layer of bone shell under the periosteum, within which several cystic cavities of different sizes containing dark red hemorrhagic fluid are visible.
2.Microscopy
Aneurysmal bone cysts are well-defined and consist of blood-filled cavities spaced by fibrous connective tissue. The fibrous septa are composed of fibroblasts, scattered osteoblast-type multinucleated giant cells and woven bone surrounding osteoblasts, and the woven bone is often distributed along the fibrous septa.
Differential diagnosis
1.Bone cysts
Most of them are located in the proximal humerus and femur. Patients have no obvious pain and swelling and are prone to pathological fracture. X-ray lesions show central osteolytic destruction with reactive sclerotic bands at the edges, and yellow serous fluid in the capsule at puncture.
2. Non-ossifying fibroma
It is usually small in size, oval and eccentric, with irregular map-like edges and obvious surrounding sclerotic bands.
3.Giant cell tumor of bone
Giant cell tumor of bone is usually seen in the age of 20-40 years, located at the end of the bone, without calcification or ossification in the lesion, and the lesion is large in scope, and there is usually no reactive sclerotic bone around it. Sometimes giant cell tumor of bone can be combined with aneurysmal bone cyst.
V. Treatment and prognosis
Osteotomy is usually performed to remove the lesion, and after scraping, local inactivation measures are used to reduce its recurrence rate. In cases with pathological fractures, internal fixation should be performed simultaneously. Deep lesions may bleed heavily during surgery and should be prepared for blood transfusion. The disease is also sensitive to radiation therapy, but it has the risk of damaging the epiphysis and causing malignant changes, so it should be used with caution.
Typical cases
Case 1: 38-year-old female with aneurysmal bone cyst in the right proximal femur, with scraping of the lesion and internal fixation of DHS
Preoperative radiograph
Preoperative CT
Postoperative X-ray
Complete healing 1 year after surgery
This article is authorized by Dr. Shiquan Zhang.