Most common primary malignant tumour of orbit is: September 2011, March 2013 (b, d)
**Core Concept**
The question is testing knowledge of orbital tumors, specifically the most common primary malignant tumor of the orbit. The orbit is a complex anatomical structure containing various tissues, including bone, muscle, and fatty tissue, which can give rise to various types of tumors.
**Why the Correct Answer is Right**
The correct answer is **Sebaceous Cell Carcinoma**. This type of tumor arises from the meibomian glands or sebaceous glands of the eyelid. It is the most common primary malignant tumor of the orbit, accounting for approximately 10-15% of all orbital tumors. Sebaceous cell carcinoma is a highly malignant tumor that can cause proptosis, eyelid swelling, and vision loss if left untreated.
**Why Each Wrong Option is Incorrect**
**Option A:** **Lymphoma** - While lymphoma can involve the orbit, it is not the most common primary malignant tumor. Lymphoma is a type of cancer that arises from lymphoid cells and can cause a range of symptoms depending on the location and extent of the disease.
**Option B:** **Rhabdomyosarcoma** - This is a type of soft tissue sarcoma that can occur in the orbit, but it is more common in children and is not the most common primary malignant tumor.
**Option C:** **Malignant Melanoma** - While melanoma can occur in the orbit, it is rare and not the most common primary malignant tumor.
**Option D:** **Adenocarcinoma** - This is a type of cancer that can occur in various tissues, but it is not the most common primary malignant tumor of the orbit.
**Clinical Pearl / High-Yield Fact**
Sebaceous cell carcinoma can be challenging to diagnose, and a high index of suspicion is required to make the correct diagnosis. Imaging studies, such as CT or MRI scans, can help confirm the diagnosis and guide treatment.
**Correct Answer:** C. Rhabdomyosarcoma