Random Dermatology MCQ - Cutaneous meningioma

A newborn is noted to have a firm, subcutaneous, skin-colored nodule in the midline of the occipital scalp at birth. The overlying skin is normal. The lesion does not transilluminate. MRI reveals a direct connection between the subcutaneous nodule and the intracranial space via a defect in the underlying calvarium. A biopsy of the cutaneous lesion shows whorled nests of oval to spindle-shaped cells with psammoma bodies. What is the most likely diagnosis?

A. Dermoid cyst
B. Encephalocele
C. Nasal glioma
D. Primary cutaneous meningioma (Type II: meningothelial hamartoma)
E. Pilomatricoma

Correct Answer: D. Primary cutaneous meningioma (Type II: meningothelial hamartoma)

Answer and Explanation

The correct answer is D. This question describes the classic presentation of a primary cutaneous meningioma (PCM), specifically the congenital Type II or meningothelial hamartoma. The key clues are the midline occipital location, the connection to the intracranial space (indicating a developmental origin from meningeal tissue trapped during closure of the neural tube), and the pathognomonic histology of whorled nests of meningothelial cells and psammoma bodies (laminated calcifications). Type II PCM is congenital and often associated with cranial defects.

Why the Other Options are Incorrect:

• A. Dermoid cyst: A dermoid cyst is a common midline lesion, but it is typically cystic and may contain hair. Histology shows a cyst wall lined by epidermis with adnexal structures, not whorls of meningothelial cells.

• B. Encephalocele: An encephalocele is a neural tube defect involving herniation of meninges and brain tissue through a cranial defect. It would contain glial tissue (GFAP-positive), not the meningothelial whorls described.

• C. Nasal glioma: This is a congenital lesion composed of heterotopic glial (brain) tissue, most commonly at the root of the nose. It is not connected to the intracranial space in most cases, and histology shows glial cells (GFAP+), not meningothelial cells.

• E. Pilomatricoma: This is a benign tumor of hair matrix origin. It is typically a hard, rock-like nodule, most common on the face and upper limbs of children, not a midline occipital lesion. Histology shows basaloid cells and "ghost" cells, not psammoma bodies.

Additional High-Yield Information for Exams:

• Classification of Primary Cutaneous Meningiomas:

  • Type I: Ectopic meningioma (most common). No CNS connection. Presents as a solitary papule/nodule on the scalp, face, or paravertebral region in adults.

  • Type II: Meningothelial hamartoma. Congenital, associated with cranial defects or sinus tracts, as described in the question.

  • Type III: CNS meningioma with direct extension to the skin. This is not primary cutaneous.

• Histopathology: The histology mirrors that of intracranial meningiomas. Key features include:

  • Whorls or nests of uniform, oval to spindle-shaped meningothelial cells with eosinophilic cytoplasm.

  • Psammoma bodies: Concentrically laminated calcifications within the whorls.

  • Immunohistochemistry: The cells are strongly positive for Epithelial Membrane Antigen (EMA) and Vimentin. They are negative for S-100 (which helps differentiate from schwannoma) and GFAP.

• Differential Diagnosis: The differential for a midline scalp nodule in a newborn/infant includes dermoid cyst, encephalocele, and PCM. Histology and imaging are definitive.

• Associated Conditions & Prognosis:

  • Benign Nature: Primary cutaneous meningiomas are almost always benign (WHO Grade I).

  • Prognosis: Excellent after complete excision. Recurrence is rare.

• Management & Rationale:

  • Rationale: The goals are to establish the diagnosis, evaluate for intracranial connection, and achieve complete excision to prevent recurrence.

  • First-line: Imaging (MRI of the brain/scalp) is mandatory to evaluate for a cranial defect and intracranial connection, which significantly impacts surgical planning.

  • Definitive Management: Complete surgical excision, often requiring a multidisciplinary approach with neurosurgery if an intracranial connection is present. For Type I lesions without connection, simple excision is curative.