Short cases – Mediastinum case 1 (FS) – NUS Pathweb

Mediastinum case 1 (FS)

Case writer: A/Prof Nga Min En

Clinical history:

18M, history of cough for 1 month
Accompanied by face and neck ‘puffiness’ and ‘feeling of pressure’ when supine
CT scan of the thorax shows a 16 x 15 x 9cm anterior mediastinal mass compression on the superior vena cava. No fat or calcification is noted.
An open incisional biopsy is performed, and sent for frozen section.
What additional clinical information would you want at the time of the frozen section?
How would you handle this fresh specimen?
What are the cytologic findings?
What are your differential diagnoses?
What ancillary tests would you do?

Click picture to enlarge

In anterior mediastinal masses that arrive fresh for frozen sections (FS), cytology samples are especially useful, in addition to the usual H+E-stained frozen sections
The following cytology smears can be prepared:
- Touch imprints (1 air-dried, 1 alc-fixed)
- Smears from scrapings (1 air-dried, 1 alc-fixed)
- The alcohol-fixed smears can be stained with H+E
Both air-dried and alcohol-fixed smears are useful
- Air-dried – for cytoplasm (e.g. scant bluish cytoplasm in lymphoma); for background material (e.g. lymphoglandular bodies; tigroid background in seminoma)

Touch imprint shows large, discohesive cells admixed with a few lymphocytes. Note how much larger the lesional cells are compared to lymphocytes.
The background shows a characteristic lacy “tigroid” appearance - this is due to glycogen from the cytoplasm.
This characteristic background is seen in air-dried smears and not alcohol-fixed smears.

In a young patient (teens or early adulthood) with an anterior mediastinal mass, the main differential diagnoses are:

Lymphoma (e.g. Hodgkin lymphoma, primary mediastinal large B-cell lymphoma, T-lymphoblastic lymphoma)
Germ cell tumour (e.g. seminoma, teratoma, non-seminomatous GCTs)

Thymic tumours may be added to the DDx list in middle-aged to older patients.

Important information that is diagnostically relevant would be:

Tumour markers e.g. b-HCG (may be mildly raised in seminoma), AFP levels
LDH – not specific; this can be raised in lymphomas as well as germ cell tumours
Radiological findings – e.g. teratomas tend to have distinctive features, with recognisable fatty, bony or calcific elements

Diagnosis

Learning Points

Differential diagnoses in anterior mediastinal masses depends on the age of the patient. Many tumours occur in young adults.
Correlation with radiologic findings and tumour markers can be very helpful.
Intra-operative cytology touch imprints and smears are very useful in evaluating frozen sections in mediastinal masses. Both air-dried and alcohol-fixed preparations should be performed, as they provide complementary information.