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frozen section

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


general rules for biopsy ***

- 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)


do hard or soft tissues need more time to fix?

hard tissue penetration rate is generally 1 mm/hr


how much fixative should be used?

10X volume of fixative over specimen volume


fixation time neutral buffered formalin

12-24 hrs


% formaldehyde neutral buffered formalin ****


(dilution from 40% aquesus solution of formaldehyde)


best fixative

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


how do you get rid of para-formaldehyde


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


steps for paraffin section

  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


how do you perform frozen section?

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


cryostat =

microtome in the freezing cabinet


indications for frozen section

  • 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


**** inappropriate specimens for frozen section


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

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