36: Surgical Pathology - Fang

Question 1

frozen section

Answer 1

• urgent need only
• not always accurate
• paraffin embedding is standard

Question 2

general rules for biopsy ***

Answer 2

• avoid necrosis and hemorrhage areas
• larger lesion –> more numerous biopsies
• ulcerated tumor –> peripheral biopsy suggested
• all fragments should be collected
• do not crush, squeeze or do cautery
• fix in fixatives ASAP if is is for paraffin sectioning
• orientating specimen eg deep margin, superior and inferior margins by using sutured threads (long, short)

Question 3

do hard or soft tissues need more time to fix?

Answer 3

hard tissue penetration rate is generally 1 mm/hr

Question 4

how much fixative should be used?

Answer 4

10X volume of fixative over specimen volume

Question 5

fixation time neutral buffered formalin

Answer 5

12-24 hrs

Question 6

% formaldehyde neutral buffered formalin ****

Answer 6

4%

(dilution from 40% aquesus solution of formaldehyde)

Question 7

best fixative

Answer 7

10% neutral buffered formalin

• satisfactory penetration into tissue
• little shrinkage
• cheap
• satisfactory hardening
• preserve fat and RBC well
• special stains can be used on tissues after fixation
• preserve color of tissue-

(-) need to be changed every 3-6 mo b/c forms formic acid

(-) can’t preserve glycogen

Question 8

how do you get rid of para-formaldehyde

Answer 8

alcohol

(para-formaldehyde (white precipitate) form when stored for long time)

Question 9

steps for paraffin section

Answer 9

1. fixation with formaliln
2. dehydration by using fradient concentrations of alcohol
3. clearing by using the flammable xylene
4. paraffin impregnation
5. embedding to make tissue as block of hard paraffin
6. sectioning (into very thin 5-8 um) in thickness using microtome)
7. attachment to slides (positive charge)
8. dewax/deparaffinization with xylene
9. staining (HE - nucleus blue/baso and cytoplasm pink/acid)
10. mounting with permount and cover slip

Question 10

how do you perform frozen section?

Answer 10

fresh tissue immediately frozen in liquid N2 and make a thin section by using cryostat

Question 11

cryostat =

Answer 11

microtome in the freezing cabinet

Question 12

indications for frozen section

Answer 12

• benign or malignant lesions
• metastatic lymph node: such as sentinel nodes in breast carcinoma
• adequacy of surgical margins
• presence or absence of ganglion cells in large intestinal wall of Hrishcsprung dz

Question 13

**** inappropriate specimens for frozen section

Answer 13

• thyroid tissue (thyroid follicular lesions are difficult to differentiate b/w benign and malignant)
• large specimens including large tumors
• highly infectious specimens (HIV)
• TB