Products of conception evacuated at 14 weeks of gestation show grape-like vesicles. Histology reveals diffuse villous oedema with central cistern formation, circumferential trophoblastic proliferation, and widespread cytological atypia. Immunohistochemistry for p57 shows complete absence of staining in cytotrophoblast and villous stromal cells. The genetic composition of this conceptus is:

• A Triploid, with one maternal and two paternal haploid genomes
• B Diploid, with one maternal and one paternal haploid genome
• C Diploid, with all chromosomes of paternal origin ✓
• D Tetraploid, with equal maternal and paternal contribution

Explanation

Loss of p57 staining indicates a complete hydatidiform mole. p57 (CDKN1B) is maternally imprinted and expressed only when a maternal allele is present, so its absence proves the entire genome is paternally derived, classically a 46,XX karyotype from fertilisation of an empty ovum by sperm followed by duplication. Partial moles retain maternal DNA, stain positively for p57 and are triploid with fetal tissue present, making option A the description of the key distractor. Normal conception retains maternal genes and stains strongly.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.