Table 2.

Differential diagnosis for Primary Osteosarcoma of the ethmoid sinus.

	Osteosarcoma	Fibrous Dysplasia	Osteoblastoma	Osteomyelitis
Plain Films	Aggressive bone tumor with cortical and medullary destruction Wide transition zone-permeative or moth-eaten appearance Aggressive periosteal reaction (sunburst type and Codman triangle)	Well circumscribed benign lesions with no cortical destruction Classically ground glass appearance. No periosteal reaction	Predominantly lytic lesions with tendency to be expansile. They may be associated with soft tissue mass and cortical destruction. 20% of the cases may be secondary to aneurysmal bone cyst	Depends on the age of the process: Normal in the first 5–7 days in children and 10–14 days in adults. Regional osteopenia initially, focal bone lysis, periosteal reaction, loss of bony trabecular architecture. In chronic cases: sequestrum, involucrum or cloaca.
CT	Adds little to plain film radiograph: except in lytic lesions. Excellent detection of tumor calcification and cortical involvement. Main role is to assist in biopsy and staging	Benign lesions with ground glass appearance but can be cystic or sclerotic. Expansion of the bone with intact overlying bone	Predominantly lytic Bone mineralization is better appreciated on CT.	Demonstration of bony margins, sequestrum/involucrum is superior to MRI and plain film.
MRI	MRI: Local staging: intraosseous tumor extension and soft tissue involvement. T1: soft tissue: intermediate signal intensity; mineralized / ossified components: low signal intensity; peri-tumoral edema: intermediate signal intensity; scattered regions of hemorrhage: variable signal, enhancement: solid components enhance T2: soft tissue: high signal intensity; mineralized / ossified components: low signal intensity; peri-tumoral edema: high signal intensity	MRI is not useful in the differential diagnosis: marked variability in the appearance of the bones lesions and often resemble tumor or more aggressive lesions.	More specific but overestimates the lesion. T1 and T2: Typically hypo to isointense with foci of decreased signal intensity corresponding to areas of calcification. C+ (Gad): Enhances avidly including the surrounding soft tissues.	More specific and sensitive in the detection of soft-tissue/joint complications. T1-intermediate to low signal central component (fluid); surrounding bone marrow lower signal than normal due to edema; enhancement both bone marrow, abscess margins periosteum and adjacent soft tissues. T2 -bone marrow edema central high signal (fluid)
Bone scan (Tc99m)	Increased radiotracer uptake of the tumor and metastases.	Increased radiotracer uptake.	Often shows intense uptake	Increased radiotracer uptake.