Introduction

Dorn Spinal Therapy

Spine Healing Therapy

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A focal region of radiolucency, or "cystic" lesion occurs when there is disruption of the steady state between bone formation and bone resorption. Matrix deposition, abnormal metabolic activity, or increased blood flow all may lead to these focal areas of osteolysis.

There is a spectrum of lytic lesions ranging from primary malignant tumors and metastases to subarticular geodes and unicameral bone cysts (Fig. 1 ). Biologically aggressive lesions show an irregular appearance, with poorly defined margins and a broad interface. Less aggressive lesions are termed bony cysts, with homogeneous lysis, well-defined sclerotic or nonsclerotic margins, cortical bone thinning without destruction, and, in some cases, fluid-fluid levels on computed tomography (CT) or magnetic resonance imaging (MRI).

Occasionally, conventional imaging may yield a specific diagnosis. In many cases, however, more advanced imaging or even percutaneous biopsy is required.

I recommend treating many types of lytic bone lesions to avoid potential pathological fractures.

Histologically there are three types of bone cysts, the simple bone cyst containing serofi-brinous fluid, the ganglion or synovial cyst with mucinous material, and the aneurysmal bone cyst (Fig. 2 ), with central blood products. Because the central fluid is produced by the outer capsule, this fluid, to some degree, reflects the biologic behavior—serofibrinous in areas of low activity, mucinous in lesions with medium activity, and hemorrhagic in active processes.

Cysts require treatment following fracture when thought to be at risk for pathologic fracture, or when symptomatic. The classic therapy has been surgical resection of the membrane with internal bone grafting. Occasionally, the adjacent bone is inadequate to support the load without metallic fixation. Also, recurrence can occur when the capsule is incompletely resected.

An alternative treatment, after aspirating to confirm the presence of fluid, is to lyse the capsule and stimulate new bone production. These objectives can be achieved via controlled ischemia or foreign body-induced inflammation.

This ischemia is created iatrogenically by obstructing the blood supply or via the use of irritating chemical products.

Arterial coils can be placed to interrupt the blood flow to the lesion. This technique historically has had limited value due to the scarcity of large feeding vessels in these lesions and is currently considered obsolete. The notable exception is aneurysmal bone cysts. In this situation very selective embolization may be performed. To obtain effective and maintained ischemia, I recommend the use of metallic coils rather than particles. This method is technically difficult in younger patients.

An alternative procedure is to directly inject particles into the lesion, also with the intention of provoking ischemia. The site of puncture is selected utilizing CT guidance. Similar to feeding-vessel embolization, this technique has had limited success.

Method: Angiography with selective examination.

Materials: 18-gauge needle, 5 F catheter, and others for selective examination. Particles or metallic coils.

Remarks: Most useful in very highly vascularized lesions such as anuerysmal bone cysts. Follow-up shows progressive thickening of the wall.

FIGURE 1 (A) Anteroposterior X-ray view with pathological fracture through a cystic lesion. (B) Axial computed tomography of the iliac bone. Proved simple cyst involving the posterior iliac spine. (C) Axial gradient echo T2W image of the iliac and sacrum. A high-signal cyst is indentured in the ilium. The additional focal area of marrow edema in the anterior sacrum (C) may be the result of altered mechanics and bone weakening. Cyst with cortical expansion.

FIGURE 1 (A) Anteroposterior X-ray view with pathological fracture through a cystic lesion. (B) Axial computed tomography of the iliac bone. Proved simple cyst involving the posterior iliac spine. (C) Axial gradient echo T2W image of the iliac and sacrum. A high-signal cyst is indentured in the ilium. The additional focal area of marrow edema in the anterior sacrum (C) may be the result of altered mechanics and bone weakening. Cyst with cortical expansion.

FIGURE 2 (A) Axial computed tomography scanner of an aneurysmal bone cyst in the left iliac wing with fluid-fluid levels. Inset shows angiography and coil embolization. (B) Direct puncture of a cyst-like lesion involving the sacrum.

FIGURE 3 (A) Anteroposterior view of the proximal humeral shaft showing a typical single bone cyst filled with iodinated contrast after the puncture with a 20-gauge needle. (B) Same patient one month later, after one dose of 160 mg methyl methacrylate and prednisolone injection. Note the sclerotic margin and visible blood vessels. (C) End result of the treatment three months later.

FIGURE 3 (A) Anteroposterior view of the proximal humeral shaft showing a typical single bone cyst filled with iodinated contrast after the puncture with a 20-gauge needle. (B) Same patient one month later, after one dose of 160 mg methyl methacrylate and prednisolone injection. Note the sclerotic margin and visible blood vessels. (C) End result of the treatment three months later.

Indirect chemical techniques are more effective than direct vascular ones. These products destroy the capsule and stimulate new bone formation. This occurs secondary to a combination of ischemia, inflammation, and direct toxicity.

The first products employed for the direct treatment of the cysts were various types of corticosteroids. We currently use methylprednisolone acetate (Fig. 3). This treatment was originally described as an operative procedure but may be performed percutaneously in a fluoroscopy suite.

The direct puncture should be made with a fine needle (18- to 20-gauge). First the periosteum is anesthetized, and then the superior aspect of the lesion is localized. The needle is then advanced into the cavity, utilizing a twisting maneuver. An additional needle may be placed to ensure ease of aspiration. In either situation, the cyst fluid is initially aspirated and evaluated visually and via cytology. This technique can be used in long-bone cysts, juxtarticular cysts, and in the spine.

During or before the procedure, iodinated contrast should be injected to determine the size and number of cavities within the cyst. It is important to compare these images with available cross-sectional studies to be sure that all parts of the lesion are accessible from the initial puncture. It is mandatory to fill all cyst loculations. If areas are not visualized on the initial contrast injection, performance of a second or third puncture may be necessary. Failure of the steroid to completely fill the lesion is an important cause of recurrence.

The approximate dose is 160 mg for each injection and three of them are carried out at one-month intervals. The steroid injection produces capsular thickening with hyperemia as seen on contrast-enhanced MRI. It is believed that the hyperemia leads to an uncoupling of the osteoclast-osteoblast balance, with the result being new bone formation.

Normally for patient follow-up, we utilize conventional radiography (Fig. 4). When planning a second steroid dose, iodinated contrast is injected into the lesion. When effective, the treatment produces capsular thickening and visualization of collateral circulation.

The corticosteroid dose rarely leads to side effects or adverse reactions (Fig. 5 ). Recurrences do occur, often related to incomplete filling. These recurrences are somewhat more frequent in the calcaneous and with very large cysts. The incidence of recurrence is decreased when opacifi-cation of all components of the lesion is verified prior to treatment. The best results are obtained in younger patients.

Method: Local anesthesia is provided and a direct puncture is made in the superior region of the lesion. Usually a handheld drill is sufficient. All loculations must be filled with iodinated

FIGURE 4 (A) Anteroposterior (AP) X-ray view of the forearm showing a typical single bone cyst. The cortical bone shows areas of endosteal scalloping corresponding with the cyst loculations. (B) AP X-ray after treatment, confirming the cyst size with iodinated contrast injection around the lesion. (C) Coronal SE TIW image after gadolinium injection. A thick capsule is noted.

FIGURE 4 (A) Anteroposterior (AP) X-ray view of the forearm showing a typical single bone cyst. The cortical bone shows areas of endosteal scalloping corresponding with the cyst loculations. (B) AP X-ray after treatment, confirming the cyst size with iodinated contrast injection around the lesion. (C) Coronal SE TIW image after gadolinium injection. A thick capsule is noted.

FIGURE 5 (A, B) Computed tomography (CT) and anteroposterior (AP) X-ray view of a typical single bone cyst involving the femoral neck. (C, D) AP X-ray view and CT-after to assess the cyst capacity following steroid treatment. Absence of bone answer or capsular thickening.

contrast. If necessary, each loculation might require a separate puncture. To avoid pain, the author recommends placing two needles. After treatment, the patient should rest for one to two hours.

Materials: 18 to 20-gauge needles, local anesthesia, iodinated contrast, and methylprednisolone acetate, 160 mg for each puncture. Remarks: Steroid injection is a very safe procedure with few side effects and is useful in intermediate-sized lesions. This treatment is recommended for simple bone cysts. Recurrences can be minimized with attention to technique.

An alternative to steroid injection is bone marrow injection into the cyst. The marrow can be obtained from the patient's iliac crest and directly injected into the lesion. This treatment produces an osteoblastic reaction through a nonspecific mechanism. This technique can be used as a second-line procedure in the event of recurrence (Fig. 6).

In cases of recurrence, instead of marrow injection, or in very active lesions, alcohol may be injected. Using this method, scarring and chemical irritation to the capsule is produced with resultant thickening.

Absolute alcohol can be used in adults (Fig. 7). Or as an alternative, Ethibloc® composed of corn protein and ethanol, can be injected. The Ethibloc causes a foreign body reaction inflammatory response with the result also being capsular thickening.

These are the preferred treatments in areas where the steroids are not effective, such as the calcaneous and in very active or large simple or aneurysmal bone cysts. The author prefers the use of Ethibloc in pediatric patients as well. Theoretically, this is less dangerous than the absolute alcohol because of its increased viscosity.

No precise Ethibloc dose is accepted, but an excessive dose can produce serious inflammatory side effects. Because the therapeutic effect is based on hyperemia, there is a fairly narrow window between positive increase in blood flow and pathologic hyperemia (Fig. 8 ). We recommend follow-up MRI examinations to assess the extent of the inflammatory reaction. An aseptic abscess can also appear following Ethibloc injection.

Method: Direct puncture, avoiding areas of cortical destruction. If Ethibloc extravasates, a soft-tissue granuloma can form. A baseline contrast injection should be performed to determine the number of lobules. Careful dose titration and only partial cyst filling should be attempted. Materials: Local anesthesia, iodinated contrast, 14-gauge needle, and Ethibloc. Remarks: The Ethibloc is a quick and useful treatment in many cases and leads to rapid wall thickening. Failures, however, can occur.

FIGURE 6 (A) Anteroposterior (AP) X-ray view of the femoral neck after a steroid treatment, previously seen in Figure 5. Note the absence of the thick wall. (B) AP X-ray view, one month after repeat bone marrow injection. Note the development of a thick capsule and new vessels.

FIGURE 7 (A) Computed tomography of calcaneous bone showing an expansile, low-grade single bone cyst. (B) One month after 4-cc alcohol injection. Single bone cyst with thick walls due to a granulomatous reaction. Magnetic resonance imaging confirmed the thickening of the cyst wall.

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FIGURE 8 (A) Computed tomography of the proximal toe phalange. Fluid-fluid level in aneurismal bone cyst. (B) Sagittal T2W magnetic resonance imaging (MRI) shows a lobulated expansile lesion. (C) One month after Ethibloc injection, showing prominent wall thinning. (D) T1W MRI image also shows cortical disruption with a soft-tissue mass.

FIGURE 9 (A) Single bone cyst injected with iodinated contrast to evaluate the size prior to treatment. (B) Radiograph one month after ethanol treatment shows a marked decrease in cyst size, with visualization of large draining veins. (C) Computed tomography shows wall thickening. (D) Magnetic resonance imaging, GRE image. Shows central reactive tissue.

FIGURE 9 (A) Single bone cyst injected with iodinated contrast to evaluate the size prior to treatment. (B) Radiograph one month after ethanol treatment shows a marked decrease in cyst size, with visualization of large draining veins. (C) Computed tomography shows wall thickening. (D) Magnetic resonance imaging, GRE image. Shows central reactive tissue.

Mucinous cysts, juxta-articular ganglions, and large anuerysmal and simple bone cysts respond well to alcohol installation (Fig. 9 ). The ethanol provokes an inflammatory reaction, obliteration of blood vessels, and tissue necrosis.

Extreme care must be used when the lesion is close to the articular surface, because intra-articular alcohol can destroy cartilage and, potentially, the synovium. A baseline contrast injection is performed again in this situation to confirm that the cyst does not communicate with the joint surface.

In cases of ganglion cysts, we initially aspirate, and then inject a local anesthetic with a 14-gauge needle to decrease the viscosity of the lesional matrix. The alcohol is then administered by means of puncture with a 14- to 20-gauge needle. The recommended dose is 3 to 5 cc injected slowly to avoid pain, under fluoroscopic guidance.

MRI performed after alcohol injection will show perilesional bony edema and extensive capsular thickening (Fig. 10 ). Over time, the cavity will fill in with fibrous tissue and enhancement will decrease.

Usually the results of alcohol injection are excellent.

FIGURE 10 (A and C) Magnetic resonance imaging (MRI) Sagittal view TIW and T2W images, juxta-articular cyst without reactive perilesional edema. (B) Computed tomography shows the margins of the lesion. (D) MRI following alcohol treatment shows the new perilesional edema and thickening of the lesion capsule.

FIGURE 10 (A and C) Magnetic resonance imaging (MRI) Sagittal view TIW and T2W images, juxta-articular cyst without reactive perilesional edema. (B) Computed tomography shows the margins of the lesion. (D) MRI following alcohol treatment shows the new perilesional edema and thickening of the lesion capsule.

Method: Local anesthesia and often sedation are administered. Slow injection with a thin needle under fluoroscopic guidance to verify that all lobules are filled. Materials: 14- to 20-gauge needle, local anesthesia, sterile absolute ethanol, and fluoroscopy. Remarks: Alcohol injections yield rapid results with moderate risk. This method is best used for synovial and aneurysmal bone cysts.

As an alternative treatment for the juxta-articular ganglion, cement can be injected (Fig. 11). The increasing use of vertebroplasty has allowed the diffusion of cement handling skills and the development of kits for its injection. This is a very attractive treatment in those cases that merit rapid increase in the adjacent bone's resistance to stress and trauma. Similar to alcohol, methyl methacrylate is chondrotoxic. Therefore when lesions are juxta-articular we have utilized synthetic hydroxyapatite as an alternative. This injection is similar to bone cement and we use the same equipment as that used in vertebroplasty, including the needle and injector device. The advantage of hydroxyapatite, in contrast to the acrylic products, is the absence of exothermic reaction; however one loses the immediate strength available via cementoplasty, although both products are able to decrease the articular pain promptly.

To fill the cavity we must prepare the cement after evaluating the capacity of the cyst and observing for possible local leakage of iodinated contrast.

The use of a nonexothermic material allows us treat safely spinal lesions that have broken the posterior wall of the vertebral body (Fig. 12). The preliminary results are suggestive of success, and with this method we may treat more degenerative cysts.

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FIGURE 11 (A, B) Juxta-articular ganglion, filled with acrylic cement. (C, D) Juxta-articular ganglion, filled with synthetic hydroxyapatite.

Method: The paste must be injected using needles and vertebroplasty instruments. The puncture should avoid nerve roots and important vessels, deep analgesia is necessary.

Materials: Surgical acrylic cement or synthetic hydroxyapatite. 14-gauge needles.

Remarks: Sometimes it is better to fill the cavity with a solid product, especially in lesions close to the articular surface. We can use acryclic bone cement, but this material produces an increase in local tissue temperature that can be dangerous to the articular surface. To avoid chondrolysis we can use synthetic hydroxyapatite, a biologically well-accepted material without chondral toxity. The selection of the product to be injected can be determined after the extent and location of contrast extravasation is noted.

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FIGURE 12 (A) Computed tomography of ABC. Vertebral body and posterior arch are involved. (B) One month later, the vertebral body becomes partially ossified. (C) Two months later, the soft-tissue component and posterior arch begin to be ossified.

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