WBR0202

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pathology
Sub Category	SubCategory::Oncology
Prompt	[[Prompt::A 9-year-old boy is brought to the pediatrician's office for persistent pain in his right leg. The mother explains that the patient's symptoms have been progressively worsening for the past 2 months. Upon further investigation, the patient reports recent unintentional weight loss despite normal appetite. Physical examination is remarkable for tenderness over the right femoral diaphyseal area. Additional testing reveals a right femoral bone mass with a histopathological analysis that demonstrates small, round, blue cells that are CD99-positive. What is the most likely radiographic finding of this patient's right femur?]]
Answer A	AnswerA::Double-bubble sign
Answer A Explanation	[[AnswerAExp::Double-bubble sign is a feature of osteoclastoma. Osteoclastoma often affects older patients (20-40 years) and is usually located at the epiphysis of long bones.]]
Answer B	AnswerB::Punched-out erosions with over-hanging cortical bone
Answer B Explanation	[[AnswerBExp::Punched-out erosions with over-hanging cortical bone (rat-bite erosions) are characteristic of gout. Gout is an acute monoarthritis caused by precipitation of the needle-shaped, negative-birefringent monosodium urate (MSU) crystals. It is associated with hyperuricemia and results in podagra, a painful MTP joint of the big toe.]]
Answer C	AnswerC::Onion-skin appearance
Answer C Explanation	AnswerCExp::Onion-skin appearance is a radiographic finding commonly observed in Ewing's sarcoma.
Answer D	AnswerD::Glistering mass within the medullary cavity
Answer D Explanation	[[AnswerDExp::Glistering mass within the medullary cavity is a feature of chondrosarcoma. Chondrosarcoma affects men between the ages 30-60 years and commonly develops in the pelvis, spine, scapula, tibia, and femur.]]
Answer E	AnswerE::Erlenmeyer flask deformity
Answer E Explanation	[[AnswerEExp::Erlenmeyer flask appearance is a feature of osteopetrosis (stone bone/ marble done disease/ Albers-Schönberg disease). Osteopetrosis is characterized by dense, thick bones due to impaired osteoclastic resorption activity.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Ewing’s sarcoma is an aggressive poorly-differentiated bone and soft tissue cancer of childhood. It is usually caused by a translocation between chromosomes 22 and 11 (t11;22), where an oncogenic fusion of EWS gene on chromosome 22 to an Ets factor (usually FLI1 on chromosome 11) results in the expression of a potent transcription factor and initiates oncogenesis. Although Ewing's sarcoma is a rare disease, it is considered the second most common primary bone tumor, accounting for 5% of all childhood tumors. It has a male predominance, and it commonly affects the Caucasian population. The majority of patients with Ewing's sarcoma present with tumor-associated symptoms, including pain, swelling, fracture following minimal trauma, or palpation of firm solid mass. Constitutional symptoms may also be present, where patients may also complain of low-grade fevers and unintentional weight loss. Ewing's sarcoma commonly affects the metaphysis and diaphysis of lower-extremity long bones, such as the femur and tibia, or flat bones, such as the pelvis, ribs, and scapula. On imaging, Ewing's sarcoma appears as a destructive, infiltrative lesion with occasional presence of a laminated onion-skin appearance due to periosteal reaction formation. Other radiographic findings, such as sunburst/hair-on-end/spiculated appearance (periosteal reaction) and Codman triangle (raised periosteum), may also be present in Ewing's sarcoma, although they have been classically associated with osteosarcoma. On biopsy, tumor cells have a characteristic small, round blue appearance, which are almost always CD99 positive. Although Ewing's sarcoma is a rapidly growing tumor associated with high aggressiveness and poor prognosis, it is often chemotherapy-sensitive. Educational Objective: Ewing’s sarcoma is an aggressive poorly-differentiated bone and soft tissue cancer of childhood. It is usually caused by a translocation between chromosomes 22 and 11 (t11;22). Ewing's sarcoma commonly affects the metaphysis and diaphysis of lower-extremity long bones, such as the femur and tibia, or flat bones, such as the pelvis, ribs, and scapula. On imaging, Ewing's sarcoma appears as a destructive, infiltrative lesion with occasional presence of a laminated onion-skin appearance due to periosteal reaction formation. On biopsy, tumor cells have a characteristic small, round blue appearance, which are almost always CD99 positive. References: Balamuth N, Womer RB. Ewing's sarcoma. Lancet Oncol. 2010;11:184-92. Jedlicka P. Ewing sarcoma, an enigmatic malignancy of likely progenitor cell origin, driven by transcription factor oncogenic fusions. Int J Clin Exp Pathol. 2010;3(4):338-47. First Aid 2014 page 404]]
Approved	Approved::Yes
Keyword	WBRKeyword::Ewing’s sarcoma, WBRKeyword::Diaphysis, WBRKeyword::Femur, WBRKeyword::Onion-skin appearance, WBRKeyword::Femoral x-ray, WBRKeyword::X-ray, WBRKeyword::Radiographic finding, WBRKeyword::Bone tumor, WBRKeyword::Translocation, WBRKeyword::t(11;22), WBRKeyword::EWS, WBRKeyword::Bone pain
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