**Question:** Investigation of choice for soft tissue sarcoma is -

A. Chest X-ray
B. Computed tomography (CT) scan
C. Magnetic resonance imaging (MRI)
D. Ultrasonography

**Core Concept:**
Soft tissue sarcomas are malignant tumors that arise from mesenchymal cells, such as fibroblasts, myocytes, and adipocytes. The choice of investigation depends on the suspected location, size, and suspected origin of the sarcoma.

**Why the Correct Answer is Right:**
For soft tissue sarcoma, MRI is the preferred imaging modality due to its superior soft tissue contrast resolution compared to the other options. MRI is particularly useful in detecting deep or large tumors, assessing tumor infiltration into adjacent structures, and evaluating the tumor response to therapy.

**Why Each Wrong Option is Incorrect:**
A. Chest X-ray: Chest X-ray is primarily used for detecting lung lesions and pleural involvement, not soft tissue sarcomas. Soft tissue sarcomas have different imaging characteristics than lung lesions, making this option less suitable.
B. Computed tomography (CT) scan: While CT scans are useful for detecting bone lesions and assessing bony involvement, they are less sensitive for soft tissue sarcomas compared to MRI. MRI is more effective in assessing soft tissue involvement and response to therapy.
C. Ultrasonography: Ultrasonography is a useful tool for superficial soft tissue lesions and fluid collections but is less sensitive in detecting deep or large soft tissue sarcomas compared to MRI.

**Clinical Pearl:**
MRI is crucial for the initial staging of soft tissue sarcomas as well as monitoring response to therapy. It allows detailed assessment of soft tissue, bone, and adjacent structures, making it the preferred modality for this purpose.