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NBME 21 Answers

nbme21/Block 4/Question#36

A 45-year-old man comes to the physician because of ...


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If you were stuck between Chondrosarcoma(malignant) and Enchondroma(benign) remember enchondromas may erode the cortex but can never invade/disrupt the cortex. I think this was the distinction the question was testing.

Also FA 2019 456-457 says chondromas : medulla of small bones of hand and feet vs. chondrosarcoma: medulla of pelvis, proximal femur and humerus (-->our pt with thigh pain)

+1/- almondbreeze(5),

 +6  upvote downvote
submitted by neonem(302),

In addition to beeip's comments, FA2018 says that chondrosarcoma is more common in the "medulla of pelvis and central skeleton" while chondromas are more in the small bones of hands & feet... so I guess you could go off of it being in a bigger bone (femur). Or perhaps the pleomorphic histology of the cells, which would be more characteristic of a malignant tumor.

 +4  upvote downvote
submitted by beeip(76),

This review suggests that enchondroma and chondrosarcoma are unable to be differentiated on histology alone. According to Orthobullets:

"unlike enchondroma, most chondrosarcomas have non-mechanical pain (rest pain and nocturnal pain)"

Guess this diagnosis is made on history.

Chondrosarcoma = mainly affects the axial skeleton than the appendicular skeleton

Enchondroma = mainly affects the hands and feet; are cyst like

 +0  upvote downvote
submitted by aesalmon(40),

I went back and watched this section on pathoma after getting the question wrong - Dr. Sattar says that Chondromas and Chondrosarcomas arise in the MEDULLA, and not the cortex. However the question stem states that there is "thickening of the diaphysis and disruption of the CORTEX with focal area of increased calcification", ???

yotsubato  It arises in the medulla and *passes* through the cortex because its invasive and malignant. +2  

 +0  upvote downvote
submitted by burak(11),

It's hyaline cartilage, so we need the choose enchondroma or chondrosarcoma.

1- I think there are mitoses and some pleomorphic changes in slide, so it' like malignant.

2- Enchondromas are found in small bones of hand and feet according the FA, but chondrosarcomas are mainly arised in medulla of pelvis or central skeleton.

3- I wrote on my FA "Neoplastic chondrocytes in hyaline cartilage matrix WITH SMALL CALCIFICATIONS". I don't know where it is from but probably UW.

jakeperalta  Lol I've scribbled down the same thing in FA. It's UW. +