Radiopaedia Blog: Radiology signs

There are many potential causes of a cerebral ring enhancing lesion and remembering them all can prove tricky. Well, that is unless you know the very handy and aptly named MAGIC DR mnemonic. 

• M - Metastasis
• A - Abscess
• G - Glioblastoma multiforme
• I - Infarct (subacute phase)
• C - Contusion

• D - Demyelinating disease (eg. tumefactive MS)
• R - Radiation necrosis

Although you can’t possibly know by looking at the single images, for what it is worth, the above cases are; A = metastasis, B = abscess, C = radiation necrosis, D = GBM, E = demyelination, F = contusion.

This case demonstrates the typical circumferential calcification and lucent center of myositis ossificans. The imaging diagosis is not always as clear-cut as it is in this case, and further imaging may be needed. It is important to avoid biopsy of these lesions, especially in the early prolifferative phases, as histologically myositis ossificans can appear similar to osteosarcoma, and lead to inappropriate management. A clinical history of trauma, even minor trauma, can be very helpful.

• Double PCL sign - appears on sagittal MRI images of the knee when a bucket-handle tear of a meniscus (most commonly the medial meniscus) flips into the intercondylar recess and comes to lie anteroinferior to the posterior cruciate ligament (PCL) mimicking a second smaller PCL.

• Spinnaker sign - a neonatal chest radiograph sign of pneumomediastinum. It refers to the thymus being outlined by air with each lobe displaced laterally like spinnaker sails. This appearance may also be termed the thymic wing sign. Bonus radiology signs also demonstrated in this case include left-sided deep sulcus sign of pneumothorax and continuous diaphragm sign of pneumomediastinum. 

1. Lamellated, layered or onion skin
   • Commonly associated with Ewing sarcoma, but may also be seen in osteosarcoma, langerhans cell histiocytosis or acute osteomyelitis. 
2. Codman triangle
   • Commonly associated with osteosarcoma, but may also be seen in Ewing sarcoma, osteomyelitis, and a variety of other conditions less commonly.
3. Solid
   • Indicative of a slow, benign processes, a solid periosteal reaction is characteristically seen with osteoid osteoma (my favorite tumor) and stress fracture, but may be a feature of many other osseous pathologies. 
4. Spiculated, sunburst or hair on end
   • This periosteal reaction indicates a rapidly progressive underlying pathology, and is characeristic of Ewing sarcoma (and PNET), osteosarcoma, and a variety of metastatic lesions. 

General consideration

Although periosteal reactions may be seen in young and adult populations, the relatively loose attachment and active physiology of the periosteum in children leads to an earlier and more robust reaction to underlying pathology, and is a more sensitive indicator of disease. Lack of a periosteal reaction in adults, who have a tightly adhered and relatively inactive periosteum, is not unusual, even with highly aggressive underlying pathologies. (see the example of adult primary osteosarcoma at the bottom of this post) 

Diagram

Primary osteosarcoma in an adult male. Note the absence of a periosteal reaction.