Monday, April 27, 2015

Bone Tumors

Bone tumors have several features that are characteristic and can be used to narrow a differential diagnosis for a suspicious lesion. This table is by no means comprehensive but it is meant to be a quick reference for various benign and malignant osseous lesions. The following features are relevant: patient age, lesion borders, location within bone, bones, involved, bone matrix changes, periosteal reaction, matrix mineralization, and soft tissue component.

The patients can be divided into two groups based on age: younger than 30 vs older than 30. The lesion borders can be described as a narrow zone of transition (the border is easy to define) vs a broad zone of transition. Periosteal reactions can be described as thin, thick, lamellated, hair-on-end, sunburst, or Codman's triangle. Matrix mineralization is either chondroid (rings and arcs) or osteoid (cloud-like). A soft tissue component is either present or absent.

Diagnoses Age Bones Borders Physis? Cortex? Periosteal Reaction Matrix Mineralization Soft Tissue Mass
Fibrous Dysplasia under 30 Face, ribs, femur Narrow Metadiaphysis No No No No
Eosinophilic granuloma under 30 Face, humerus, ribs, femur Narrow Metadiaphysis Possible Variable No Yes, if fx
Osteoid osteoma under 30 Long bones Narrow Metaphysis Yes No No No
Nonossifying fibroma under 30 Distal femur, distal tibia Narrow Metaphysis Yes No No No
Simple Bone Cyst under 30 Proximal humerus, proximal femur Narrow Metaphysis No No No No
Osteochondroma under 30 Distal femur, proximal tibia Narrow Metaphysis Yes No No No
Ewing Sarcoma under 30 Long bones, ribs Broad Diaphysis Yes Lamellated No Yes
Osteosarcoma under 30 Long bones Broad Metaphysis Yes Sunburst, hair-on-end, Codman's Osteoid Yes
Enchondroma under 30 Small bones Narrow Metadiaphysis Yes No No No
Aneursymal Bone Cyst under 30 Posterior vertebrae, flat bones, long bones Narrow Epiphysis Yes Yes No No
Chondromyxoid fibroma under 30 Long bones Narrow Metaphysis Yes No Chondroid No
Chondroblastoma under 30 Distal femur, proximal humerus Narrow Epiphysis Yes No Chondroid No
Osteomyelitis any age Any Broad Any Yes Thick No No
Myeloma over 30 Any Narrow Metadiaphysis Yes No No No
Geode over 30 Periarticular Narrow Epiphysis Yes No No No
Hyperparathyroidism over 30 Any Narrow Metadiaphysis Thinned No No No
Giant Cell Tumor over 20 Knee, distal radius, sacrum Narrow Epiphysis No No No Eggshell ossification

Bone Tumors By Location


Monday, April 20, 2015

How To Place A Percutaneous Gastrostomy Tube

Gastrostomy tubes and their variants can be placed endoscopically, surgically, or percutaneously. The interventional radiologist can help determine which approach is best for patients. In particular, patients with pharyngeal issues, such as head and neck cancers, are good candidates for percutaneous placement. Here is one approach, which utilizes a Wills-Oglesby pigtail gastrostomy tube.

  1. Verify an appropriate window for the gastrostomy tube on pre-procedure imaging. In particular, make sure that the transverse colon does not lie between the anterior abdominal wall and the stomach.
  2. Check if the patient has a nasogastric tube. If not, using anesthetic gel and a glidewire, a Kumpe catheter can be fluoroscopically guided into the stomach. Have an assistant use the tube to insufflate the stomach.
  3. Once the stomach is sufficiently inflated, anesthetize the skin. A good location is midway along the greater curve as the passes will aim towards the fundus.
  4. A fastener is used to enter the stomach and pull it up towards the anterior abdominal wall. The introducer needle is used to initially access the stomach. Attach contrast to the needle and advance the needle under fluoro. Watch it tent the gastric wall, and then enter the gastric lumen. Intraluminal position can be confirmed by seeing the needle tip move freely, aspiration of gas, and injection of contrast outlining gastric rugae.
  5. Once intraluminal position is confirmed, the fastener is advanced through the needle, the needle withdrawn, and the fastener pulled back to lift the stomach up. If additional fasteners are desired, repeat Step 4.
  6. After the stomach is fastened, make a dermatotomy and then pass another needle into the stomach. Confirm intraluminal position as in #4. Pass a 0.035 inch wire into the stomach and watch it coil around the greater curvature past the fasteners.
  7. Withdraw the needle and serially dilate over the wire up to the size of the catheter. Work quickly as the stomach will begin to lose gas and deflate.
  8. Insert the catheter, withdraw the wire, pull the string to pig the catheter, and inject contrast to confirm final position. Suture the catheter into place. 

One protocol to clear the gastrostomy tube is to wait one day, then check the patient. If the patient is afebrile, without leukocytosis, and without peritoneal signs, start trial feeds. If the patient tolerates the trial feeds well after another day, clear the tube for full feeds.

Monday, April 6, 2015

Measurements in Interventional Radiology

Wires, catheters, and devices often have many measurements associated with them. These can often be confusing as each type of device uses its own measurement with its own unit. This post goes over some of the basic measurements one may encounter in the interventional radiology suite.

Needle Measurements

Needles, specifically hypodermic needles, are measured in a unit termed "gauge" (abbreviated G).  Unlike other measurements, a higher gauge number indicates a smaller needle. The gauge refers to the outer diameter. Typical needles encountered in IR include a 21 G needle to do micro puncture access, a 19 G needle to do direct access or transjugular liver biopsies, and 18 G needles to draw up medications. As an example, a 21 G needle has an outer diameter of 0.03225 in (0.8192 mm) and an inner diameter of 0.02025 in (0.514 mm). For more detailed measurements, see this needle gauge chart

Wire Measurements

Guide wires are typically measured in inches of thickness. Using the example above for a 21 G needle, one can see that an 0.018 inch wire can pass through a 21 G needle, because 0.018 inches is less than the inner diameter of 0.02025 inches. Similarly, an 0.035 inch guide wire can pass through a 19 G needle. For more detailed comparisons of wires, use this comparison chart to compare up to 5 wires at a time. 

Catheter Measurements

Catheters are often measured using the French scale, often abbreviated "Fr". A catheter of 1 French has an external diameter of 1/3 millimeter (mm). Therefore, a 3 Fr catheter has an external diameter of 1 mm. 

Source: "French catheter scale" by Glitzy queen00. Licensed under CC BY-SA 3.0 via Wikimedia Commons

Sheath Measurements

A sheath is used to stabilize access within a vessel. While also using the French system for catheters described above, the designation here indicates the largest French catheter the sheath will accept. So, a 6 French sheath will accept up to a 6 French catheter.

Other devices such as coils or TIPS shunts have measurements specific to them, which should be carefully considered before use.