Date: 30 September 2025

Host: Anthony Maddox (West Hertfordshire Teaching Hospitals NHS Trust)

Case 1 – Breast Cyst with Hematoidin Crystals

Patient: 66-year-old woman
History: Previous grade 3 ductal carcinoma of right breast (9 years prior). Presented with a palpable lump in left breast.
Findings:
 - Ultrasound: Small, well-defined cyst with skin discolouration.
 - Aspirate: Brownish fluid. Cytology showed hemosiderin-laden macrophages and distinctive rhomboid crystals.
 - Crystals identified as hematoidin (a breakdown product of blood, chemically similar to bilirubin).
Teaching Point: Hematoidin is a non-haem pigment (does not stain with Perl’s). Recognising it avoids unnecessary investigations.
Diagnosis: Benign breast hematoma with hematoidin crystals.

Case 2 – Axillary Lump Mimicking a Cyst

Patient: Woman with right axillary swelling
History:
 - Initial aspiration: Clear fluid (not sent).
 - Recurrence six weeks later; aspirate submitted.
Findings:
 - Cytology: Proteinaceous background with macrophages and crystalline structures.
 - Polarised light: Strong birefringence.
 - Radiology: Severe degenerative osteoarthritis of shoulder joint.
Interpretation: Crystals identified as calcium pyrophosphate (CPPD).
Teaching Point: Rare presentation of pseudogout manifesting as an axillary mass due to extension of synovial fluid from the shoulder joint.
Diagnosis: Axillary mass secondary to CPPD deposition disease (pseudogout).

Case 3 – Parotid Basaloid Tumour

Patient: 78-year-old man with parotid lump
History: Two prior FNAs reported as “salivary gland tumour of uncertain malignant potential (SUMP).” Third aspirate presented.
Findings:
 - Cytology: Basaloid cell groups, basement membrane-like globules, traversing capillaries.
 - Cell block: Some biphasic features, not conclusive.
 - Immuno:
    • CD117 negative (against adenoid cystic carcinoma)
    • SMA positive in subset of cells
    • p40 weakly positive
Discussion: Differential includes epithelial-myoepithelial carcinoma, basaloid neoplasms (basal cell adenoma, trabecular adenoma).
Outcome: Reported as basaloid tumour, suspicious for low-grade malignancy. Excision recommended.
Teaching Point: Repeat FNAs are unhelpful in persistent SUMP cases; excision or histology is required for definitive diagnosis.

Key Learning Themes

- Recognition of hematoidin is helpful and avoids confusion in haemorrhagic lesions from any site.
- Crystal identification is important and may help to support surprising diagnoses in unusual anatomical contexts.
- For FNA of salivary lesions, immunocytochemistry and cell block findings refine the differential and frequently support definitive diagnoses, but excision for both treatment and histological diagnosis may be necessary if repeated FNAs are equivocal.