## Core Concept
Sarcoidosis is a **multisystem granulomatous disease** characterized by the formation of non-caseating granulomas in various organs, most commonly affecting the **lungs**, **lymph nodes**, **skin**, and **eyes**. The etiology of sarcoidosis remains unknown, but it is believed to result from a combination of genetic and environmental factors leading to an exaggerated cellular immune response.

## Why the Correct Answer is Right
The correct answer can be deduced by understanding the common sites and manifestations of sarcoidosis. Typically, sarcoidosis affects the lungs (pulmonary sarcoidosis), lymph nodes (lymphadenopathy), skin (cutaneous lesions), and eyes (uveitis). Among the options provided, without specific details on each, we can infer based on common knowledge of the disease.

## Why Each Wrong Option is Incorrect
- **Option A:** Sarcoidosis commonly affects the lungs, making this an incorrect choice as the disease frequently involves pulmonary tissue.
- **Option B:** Lymph nodes are often involved, presenting as lymphadenopathy, which is a hallmark of the disease.
- **Option C:** The skin is a common site for sarcoidosis manifestations, including erythema nodosum and plaques.
- **Option D:** Given that the question asks what sarcoidosis doesn't involve, and without specific details on each option, we must consider which organs or systems are less commonly or not typically associated with sarcoidosis.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that **sarcoidosis can mimic other diseases** due to its wide range of manifestations, making diagnosis challenging. A classic triad for pulmonary sarcoidosis includes **bilateral hilar lymphadenopathy**, **pulmonary infiltrates**, and **eye involvement**.

## Correct Answer: D.
To accurately complete this explanation, the specific details of options A, B, C, and D are required. However, based on the general knowledge that sarcoidosis frequently involves the lungs, lymph nodes, and skin, the organ or system least likely to be involved would be the correct answer. Typically, **gastrointestinal involvement is rare** in sarcoidosis, but without explicit options, we rely on the general principle that sarcoidosis spares certain organ systems more than others.

Given the constraint and assuming a common organ not typically involved:
**Correct Answer: D.**