Dermatology MCQ - Infiltrative and Neoplastic Disorders - Conjunctival naevi

A 16-year-old patient presents for a routine eye examination. The ophthalmologist notes a well-defined, slightly elevated, variably pigmented lesion at the limbus of the left eye. The lesion contains tiny, clear cysts within it. The patient reports it has been present for as long as they can remember and has not changed. What is the most likely diagnosis and the key pathognomonic feature?

A. Conjunctival melanoma, characterized by its limbal location and variegated color.
B. Primary Acquired Melanosis (PAM), characterized by its flat, waxing and waning nature.
C. Conjunctival melanocytic naevus, characterized by the presence of intralesional cysts.
D. Pinguecula, characterized by its yellow color and location on the bulbar conjunctiva.
E. Subconjunctival hemorrhage, characterized by its bright red color and resolution over weeks.

Correct Answer: C. Conjunctival melanocytic naevus, characterized by the presence of intralesional cysts.

Answer and Explanation

The correct answer is C. This question describes a classic conjunctival melanocytic naevus. The key clinical clues are the onset in childhood, long-term stability, and the presence of intralesional cysts, which is a highly characteristic (some consider it pathognomonic) feature of a benign conjunctival nevus. The limbal location is also very common.

Why the Other Options are Incorrect:

• A. Conjunctival melanoma...: This is incorrect. Melanoma of the conjunctiva is rare, typically presents in middle-aged or older adults, and is characterized by a history of change, significant vascularity, and often arises from a precursor lesion like Primary Acquired Melanosis (PAM). The presence of cysts and long-term stability in a teenager strongly argues against melanoma.

• B. Primary Acquired Melanosis (PAM)...: This is incorrect. PAM is an acquired, flat, brown patch of conjunctival pigmentation that occurs in adults. It is characterized by its macular nature and can wax and wane. It does not form a elevated lesion with cysts. PAM is considered a potential precursor to melanoma.

• D. Pinguecula...: This is incorrect. A pinguecula is a common, benign growth of degenerated collagen on the bulbar conjunctiva, typically appearing as a yellowish, raised nodule. It is not pigmented and does not contain cysts.

• E. Subconjunctival hemorrhage...: This is incorrect. This presents as a bright red, diffuse patch of blood under the conjunctiva, which resolves spontaneously. It bears no resemblance to a stable, pigmented, cystic nodule.

Additional High-Yield Information for Exams:

• Histopathology: Conjunctival nevi are typically compound nevi (nests of melanocytes in both the epithelium and the underlying substantia propria). The pathognomonic feature is the presence of epithelial inclusion cysts within the lesion, which are lined by conjunctival epithelium and often filled with keratin. This correlates directly with the clinical finding of clear cysts.

• Differential Diagnosis: This is critical. The differential for a pigmented conjunctival lesion includes:

  • Conjunctival Naevus: As described; cystic, stable, childhood onset.

  • Primary Acquired Melanosis (PAM): Acquired, flat, patchy, brown pigmentation in adults. Lumps or nodules are absent unless it has transformed into melanoma.

  • Conjunctival Melanoma: Nodular, vascular, rapidly growing, often arising from pre-existing PAM.

  • Racial Melanosis: A bilateral, flat, brown pigmentation of the interpalpebral conjunctiva, common in darker-skinned individuals. It is symmetric and has no cysts or mass effect.

• Associated Conditions & Prognosis:

  • Benign Nature: Conjunctival nevi are benign. However, there is a very small potential for malignant transformation, much lower than the risk associated with PAM.

  • Prognosis: Excellent. The key is to document stability.

• Management & Rationale:

  • Rationale: The goal is to confirm the diagnosis and monitor for any signs of rare malignant change.

  • First-line for a classic, stable lesion: Clinical diagnosis with documentation and periodic observation. Baseline photography is extremely valuable.

  • Indication for Excision: Any sign of change is the primary indication. This includes increase in size, darkening, development of prominent vascularity, loss of cystic architecture, or involvement of the cornea. An excisional biopsy is preferred for diagnosis and treatment of suspicious lesions.

  • Biopsy: A biopsy (often an excisional one) is performed for any lesion that is not classic or shows features of concern.