Simple Bone Cyst




The simple bone cyst is a common, benign, fluid-containing lesion, usually occurring in the metaphysis of long bones. The cause of the lesion is unknown. Bloodgood recognized it as a different entity from other cystic bone lesions in 1910. [1] Jaffe and Lichtenstein provided a detailed discussion of simple bone cysts in 1942. [2] (See the images below.)

Plain radiography is the examination of choice because of its high diagnostic capability of simple bone cysts. [3, 4, 5]  Computed tomography () scanning and magnetic resonance (MRI) usually are not required and should only be used for evaluation in anatomically complex areas such as the spine or pelvis. These areas often are difficult to evaluate accurately on plain film. Use and MRI to determine the extent of the lesion and whether complications such as a fracture are present. Nuclear medicine scans usually are not necessary in the evaluation of simple bone cysts. [6, 7, 8]

Suei et al studied the relationship between the radiographic findings and treatment outcome (healing or recurrence) in 31 cases of simple bone cysts of the jaw to identify whether radiography can predict prognosis. In 17 of 31 cases, radiographic findings included preserved lamina dura adjacent to the lesion, with a smooth margin, and no or smooth bone expansion. All 17 of these lesions healed after surgery.

In the other 14 cases, there was resorption of the lamina dura, a scalloped margin, nodular bone expansion, root resorption, and a sclerotic mass or multiple cavities. In 9 of these cases, there was recurrence of bone cysts. From these findings, the authors concluded that there is a relationship between radiographic features of and prognosis and that, therefore, radiographic examination should be used not only for discovering and diagnosing such lesions but also for helping predict their prognosis. [9]

Yandow et al reported that in 5 patients who received 7 contrast injections of simple bone cysts, large and rapid outflow veins from the solitary bone cysts occurred. Precordial Doppler was able to show increased signal in all 7 particulate injections (2 steroid injections, 5 bone marrow aspirates and cyst injections.) According to the authors, Doppler may be valuable for monitoring the potential harmful effects of such injections and lead to a better understanding of failure of cyst healing because of rapid outflow of material. [10]

Radiographs demonstrate simple bone cysts as well-defined, geographic lesions with narrow transition zones. A thin sclerotic margin is a typical finding. Simple bone cysts usually are situated in the intramedullary metaphyseal region immediately adjacent to the physis. Occasionally, they may be diaphyseal. See the image below.

The long axis of the lesion parallels that of the long axis of the tubular bone. Simple bone cysts may cause expansion of the bone with thinning of the overlying cortex. Some may have a multilocular appearance. In long bones, simple bone cysts typically are centrally located within the medullary cavity. See the image below.

A pathologic fracture through a simple bone cyst is a common occurrence. This may lead to the “fallen fragment” sign, which describes the migration of a fragment of bone to a dependent portion of the fluid-filled cyst. It occurs in only a minority of patients. This sign is an important differentiating feature between a simple bone cyst and other nonlytic bone lesions. When present, the fallen fragment sign is pathognomonic of a simple bone cyst. See the image below.

Simple bone cysts occurring in the ilium may be large and radiolucent, resembling fibrous dysplasia. Lesions occurring in the spine may be localized to the vertebral body or posterior elements, and diagnosis based solely on radiographic findings is difficult.

Radiography usually is sufficient to confirm the diagnosis of simple bone cysts.

The fallen fragment sign in a cystic lesion is pathognomonic of a simple bone cyst. It indicates the internal contents of the lesion are nonsolid and fluid-filled.

Difficulty in diagnosis may arise when an enchondroma or fibrous dysplasia occurs in the metaphyseal region of a long bone in a patient in the first 2 decades of life.

CT scanning often is not necessary in the evaluation of simple bone cysts because of the high accuracy of diagnosis of radiography. CT occasionally is used in the evaluation of lesions observed in areas difficult to assess on plain radiography, such as the spine and pelvis. The role of CT is to determine the extent of the lesion as well as to detect subtle complications difficult to evaluate on plain radiography.

The features of a simple bone cyst observed on plain radiography also can be appreciated on CT. Occasionally, air and air-fluid levels may be seen within simple bone cysts. Fluid-fluid levels also may be noted. Dynamic CT scanning may help in differentiating a fluid-containing simple bone cyst, which is avascular, from other solid benign bone lesions that demonstrate varying degrees of vascularity. See the images below.

The presence of a fallen fragment sign on CT is diagnostic of a simple bone cyst. CT has high sensitivity and specificity for detecting simple bone cysts.

The presence of fluid-fluid levels within a bony lesion is not diagnostic of any particular tumor. This sign can be observed on CT in patients with fibrous dysplasia, simple bone cyst, recurrent malignant fibrous histiocytoma of bone, osteosarcoma, or aneurysmal bone cyst.

MRI can confirm the presence of fluid within a simple bone cyst. Uncomplicated simple bone cysts have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Lesions that have a pathologic fracture have heterogeneous signal intensities on both T1- and T2-weighted images because of bleeding within the cyst. With gadolinium-diethylenetriamine pentaacetic acid (DTPA) enhancement, they demonstrate enhancement with focal, thick peripheral, heterogeneous, or subcortical patterns. Septations within the lesions may be observed on MRI and may not be visualized on radiographs. See the images below. [11]

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

MRI has also been shown useful for evaluating the efficacy of intracavital injection of steroids into bone cysts. MRI reveals the presence of thin reparative tissue lining the cyst wall. This tissue progressively thickens, and new bone formation is also observed. Residual cyst cavities may also be seen with no evidence of enhancing tissue, thus requiring further treatment.

Uncomplicated lesions are diagnosed easily on MRI. Lesions complicated by pathologic fractures may reveal areas of heterogeneous signal and irregular enhancement patterns after the administration of IV contrast. This lowered specificity and sensitivity makes diagnosis more difficult.

Simple bone cysts show little or no uptake of tracer material in radionuclide bone scans unless they have been traumatized. See the image below.

Bloodgood JC. Benign bone cysts, osteitis fibrosa, giant cell sarcoma and bone aneurysm of long pipe bone. Ann Surg. 1910. 52:145-89.

Jaffe HL, Lichtenstein L. Solitary unicameral bone cyst with emphasis on the roentgen picture: the pathological appearance and pathogenesis. Arch Surg. 1942. 44:1004-25.

Brooks JK, Nikitakis NG. Incidental radiographic finding. Simple bone cyst. Gen Dent. 2008 May-Jun. 56(4):392, 395. [Medline].

Suomalainen A, Apajalahti S, Kuhlefelt M, Hagström J. Simple bone cyst: a radiological dilemma. Dentomaxillofac Radiol. 2009 Mar. 38(3):174-7. [Medline].

Kim KA, Koh KJ. Recurrent simple bone cyst of the mandibular condyle: a case report. Imaging Sci Dent. 2013 Mar. 43(1):49-53. [Medline]. [Full Text].

Buie HR, Bosma NA, Downey CM, Jirik FR, Boyd SK. Micro-CT evaluation of bone defects: Applications to osteolytic bone metastases, bone cysts, and fracture. Med Eng Phys. 2013 Jul 2. [Medline].

Faruch Bilfeld M, Lapègue F, Brun C, Bakouche S, Bayol MA, Chiavassa-Gandois H, et al. Tumors and pseudotumors of the hand: The role of imaging. Diagn Interv Imaging. 2015 Nov 9. [Medline].

Melamud K, Drapé JL, Hayashi D, Roemer FW, Zentner J, Guermazi A. Diagnostic imaging of benign and malignant osseous tumors of the fingers. Radiographics. 2014 Nov-Dec. 34 (7):1954-67. [Medline].

Suei Y, Taguchi A, Nagasaki T, Tanimoto K. Radiographic findings and prognosis of simple bone cysts of the jaws. Dentomaxillofac Radiol. 2010 Feb. 39(2):65-72. [Medline].

Yandow SM, Marley LD, Fillman RR, Galloway KS. Precordial Doppler evaluation of simple bone cyst injection. J Pediatr Orthop. 2009 Mar. 29(2):196-200. [Medline].

Sanal HT, Chen L, Haghighi P, Trudell DJ, Resnick DL. Carpal bone cysts: MRI, gross pathology, and histology correlation in cadavers. Diagn Interv Radiol. 2014 Nov. 20 (6):503-6. [Medline].

Eu-Leong Harvey Teo, MBBS, FRCR Consulting Staff, Department of Diagnostic Imaging, Kandang Kerbau Women’s and Children’s Hospital, Singapore

Eu-Leong Harvey Teo, MBBS, FRCR is a member of the following medical societies: Royal College of Radiologists, Society for Pediatric Radiology

Disclosure: Nothing to disclose.

Wilfred CG Peh, MD, MHSc, MBBS, FRCP(Glasg), FRCP(Edin), FRCR Clinical Professor, Yong Loo Lin School of Medicine, National University of Singapore; Senior Consultant and Head, Department of Diagnostic Radiology, Khoo Teck Puat Hospital, Alexandra Health, Singapore

Wilfred CG Peh, MD, MHSc, MBBS, FRCP(Glasg), FRCP(Edin), FRCR is a member of the following medical societies: American Roentgen Ray Society, British Institute of Radiology, International Skeletal Society, Radiological Society of North America, Royal College of Physicians, Royal College of Radiologists

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

Murali Sundaram, MBBS, FRCR, FACR Professor of Radiology and Consulting Staff, Cleveland Clinic Lerner College of Medicine of CWRU

Murali Sundaram, MBBS, FRCR, FACR is a member of the following medical societies: American College of Radiology, American Medical Association, American Roentgen Ray Society, Association of University Radiologists, International Skeletal Society, Radiological Society of North America, Society of Skeletal Radiology

Disclosure: Nothing to disclose.

Felix S Chew, MD, MBA, MEd Professor, Department of Radiology, Vice Chairman for Academic Innovation, Section Head of Musculoskeletal Radiology, University of Washington School of Medicine

Felix S Chew, MD, MBA, MEd is a member of the following medical societies: American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America

Disclosure: Nothing to disclose.

Giuseppe Guglielmi, MD Associate Professor of Radiology, Department of Radiology, Scientific Institute Hospital

Disclosure: Nothing to disclose.

Simple Bone Cyst Imaging

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