A groovy scapular lesion

Clinical history: A 43-year-old lady presented with 3-month history of left shoulder pain. Plain film X-ray shows a well-defined lytic lesion in the left scapula. A CT-guided core biopsy of the lesion is performed and a cytology imprint is shown.

Cytologic findings

Dispersed cell pattern
- Mostly mononuclear but may be multinucleated
- Reniform nuclei with indents, folds and grooves ("coffee-bean")
- Abundant cytoplasm with occasional phagocytosed debris
- Distinct cell borders
- Mitoses may be present but no atypical forms Scattered histiocytic cells with abundant cytoplasm
- No significant nuclear atypia
Associated with numerous eosinophils (red circles in the alcohol-fixed pic; hunt for them on the air-dried pic!)
Occasional necrosis and osteoclast-type giant cells may be seen

DDx and Immunohistochemistry

Differentials to consider:

Langerhans cell histiocytosis
Acute and chronic osteomyelitis
- Mixed inflammatory infiltrate and histiocytes
- Langerhans cells are not typically present
Granulomatous inflammation – no classical epithelioid histiocytes or well-formed granulomas

Confirmatory immunohistochemistry:

IHC interpretation:

Positive stains: S100, CD1a and Langerin
Stains to rule out differential diagnoses are usually not required

Diagnosis

Case writer: Dr Noel Chia

Musculoskeletal 1

A groovy scapular lesion