Random Dermatology MCQ - Cutaneous Meningioma

A 45-year-old woman presents with a firm, slowly enlarging, subcutaneous scalp nodule near the vertex. It is asymptomatic and has been present for several years. A biopsy reveals whorled patterns of spindle cells with psammoma bodies. Immunohistochemistry is positive for epithelial membrane antigen (EMA) and negative for S-100. Which of the following is the most likely diagnosis?

A) Cutaneous meningioma
B) Pilomatricoma
C) Neurofibroma
D) Trichilemmal cyst
E) Metastatic carcinoma

Correct Answer: A) Cutaneous meningioma

Explanation

This presentation is classic for a primary cutaneous meningioma, a rare, benign tumor derived from ectopic arachnoid cells.

Key Features of Cutaneous Meningioma:

• Clinical: A slow-growing, firm, dermal or subcutaneous nodule, most commonly on the scalp (especially near the vertex), face, or along the spine.

• Origin: Arises from ectopic arachnoid cap cells trapped during embryonic closure of the neural tube. It is not connected to the central nervous system.

• Histopathology:

  • Whorled patterns of meningothelial spindle cells.

  • Psammoma bodies: Concentric, laminated calcifications (a hallmark feature).

• Immunohistochemistry:

  • Positive: Epithelial Membrane Antigen (EMA) (this is a key diagnostic marker), Vimentin.

  • Negative: S-100 (helps rule out neural tumors), CKIT (CD117).

Why Not the Other Options?

• (B) Pilomatricoma: A benign tumor of hair matrix origin. Histology shows basophilic cells, ghost (shadow) cells, and calcification, not whorled patterns or psammoma bodies. It is often positive for beta-catenin.

• (C) Neurofibroma: A benign peripheral nerve sheath tumor. Histology shows wavy spindle cells in a myxoid matrix. It is strongly S-100 positive and EMA negative.

• (D) Trichilemmal (pilar) cyst: A common cystic lesion of the scalp. Histology shows a cystic structure lined by epithelium without a granular layer, filled with dense keratin. No whorled patterns or psammoma bodies.

• (E) Metastatic carcinoma: Would show atypical, malignant cells. The IHC profile would depend on the primary (e.g., CK7/CK20), but it would not typically show organized whorls or psammoma bodies. The benign histology and specific IHC rule this out.

Classification:
Cutaneous meningiomas are classified into three types:

1. Type I (Primary): Arises from ectopic arachnoid cells in the skin (as in this case).

2. Type II (Direct Extension): Extends from an intracranial meningioma through skull defects.

3. Type III (Metastatic): Very rare metastasis from a central nervous system meningioma.

Management:

• Simple surgical excision is curative for primary cutaneous meningiomas.

• Imaging (CT/MRI) may be considered to rule out a connection to the CNS, especially for midline lesions.

Prognosis:
Excellent; primary cutaneous meningiomas are benign and do not recur after complete excision.

Note: The combination of a scalp nodule with histology showing whorls and psammoma bodies and an EMA+/S-100- immunoprofile is diagnostic for a cutaneous meningioma. It is a great histologic mimic but has a distinct IHC signature.