**Question:** Coccidioides immitis is identified in tissues on the basis of which of the following:

a) Budding yeast cells with pseudohyphae
b) Yeast-like forms with very large capsules
c) Arthrospores
d) Endosporulating spherules

**Core Concept:** Coccidioides immitis is a fungal pathogen causing coccidioidomycosis, also known as Valley Fever. These pathogens are identified in tissues based on their distinctive morphological features.

**Why the Correct Answer is Right:**

The correct answer is option:

d) Endosporulating spherules

**Why Each Wrong Option is Incorrect:**

a) Budding yeast cells with pseudohyphae (Option A) are not characteristic of Coccidioides immitis. These features are more commonly seen in yeast cells of Candida species or some Aspergillus species.

b) Yeast-like forms with very large capsules (Option B) are not the primary morphological feature of Coccidioides immitis. Instead, endosporulating spherules are more representative of this fungus.

c) Arthrospores (Option C) are not present in Coccidioides immitis. Arthrospores are a type of spore formed by certain filamentous fungi, such as Aspergillus species.

**Clinical Pearl:**

The identification of Coccidioides immitis in tissues relies on recognizing the endosporulating spherules, which are formed when the fungus transitions from yeast-like forms to arthroconidia. These spherules are crucial for the pathogenicity of the fungus and aid in its dissemination within the host.

**Correct Answer:**

Endosporulating spherules (Option D) are the correct answer as they represent the transition form of Coccidioides immitis, which is crucial for understanding its identification in tissues. These spherules are formed when the fungus transitions from yeast-like forms.

**Explanation:**

Coccidioides immitis is a dimorphic fungus capable of switching between yeast-like forms and arthroconidia (spherules). When the fungus encounters favorable conditions in the host environment, it forms arthroconidia, which are responsible for the infection and dissemination. In tissues, these arthroconidia are referred to as endosporulating spherules, which are a crucial aspect of understanding its identification.

**Why each wrong option is incorrect:**

Option A (yeast cells with pseudohyphae) are not characteristic of Coccidioides immitis. These are typically observed in yeast cells of Candida species or certain Aspergillus species.

Option B (yeast-like forms with large capsules) are not the primary morphological feature of Coccidioides immitis. Large capsules are commonly seen in certain mucorale fungi, such as Mucor species, but not in Coccidioides immitis.

Option C (arthroconidia) is partially