A surgical sieve is useful when trying to answer questions on the cause of a sign or symptom. It helps to bring to mind lots of different conditions which could be potential causes. It can also be helpful in formulating a differential diagnosis for patients where the diagnosis is not clear.

1. SURGICAL
SEIVE

2. WHAT IT IS?
• A surgical sieve is useful when trying to
answer questions on the cause of a sign or
symptom.
• It helps to bring to mind lots of different
conditions which could be potential causes.
• It can also be helpful in formulating a
differential diagnosis for patients where the
diagnosis is not clear.

3. • A sieve allows you to gather your thoughts,
working from first principles, and come up
with at least some sensible statements. When
you answer a question, you should really talk
about the most common things first and the
rarities at the end.
• One disadvantage of using a sieve is that you
may not be able to rapidly reorganise your
thoughts in this way, but still it is useful when
all else fails and is invaluable in essay writing.

4. THE AETIOLOGICAL SIEVE
“ CAT IN CAN MED DIP”Congenital
Acquired
Traumatic
Inflammatory (physical, chemical, infective)
Neoplastic (benign or malignant, primary or secondary)
Circulatory
Autoimmune
Nutritional
Metabolic
Endocrine
Drugs
Degenerative
Iatrogenic
Psychosomatic

5. THE ANATOMICAL SIEVE
• This can apply to anatomical sites, structures or tissue
types.
• If asked ‘What are the causes of mechanical bowel
obstruction?’, you could say ‘Adhesions.’ This is a
correct answer but an incorrect way of saying it.
• Start by saying that the bowel is a structure consisting
of several anatomical regions and hence obstruction
can occur anywhere along its length, for example,
stomach outflow obstruction, small bowel obstruction
and large bowel obstruction.

6. • The examiner will then usually pick one route
and lead you along it.
• If writing an essay, you obviously need to
discuss all three.
• Then, add that the bowel is a hollow tube, and
like any hollow tube (cf. ureters) it can become
blocked at three sites: from outside the tube
pressing in (extramural), within the wall of the
tube (intramural) and within the lumen of the
tube (luminal). Where appropriate, answers
should be structured in this way.

7. Causes of Mechanical Bowel Obstruction
Extramural
Adhesions , Strangulated hernia, Volvulus,
Extrinsic compression
Intramural
Tumours, Infarction, , Strictures, Inflammation
(e.g. Crohn’s)
Luminal
Foreign body, Intussusception, Large polyps
Impacted faeces

8. GENERAL AND SPECIFIC
• Tell me about postoperative complications.
• Here, we can use two types of classification: one
applies to the type of complication, and the other
gives a time scale.
• Postoperative complications can be generalized,
i.e. applying to any operation (such as the effects
of anaesthesia), or specific, i.e. applying to a
particular operation (such as damage to the
recurrent laryngeal nerve in thyroidectomy).
• Once classified into general and specific the
complications can be broken down further into
time scales. These complications can be
immediate, early or late.

9. Once you use these principles, it becomes easy
to answer most questions logically.
For example: ‘What are the causes of
haematuria?’ The causes can be generalized
(e.g. a bleeding disorder or use of
anticoagulants) or specific, relating to any of
the anatomical structures in the region. The
following structures (starting from the top) are
part of the urinary tract:

10. Structure Causes
• Kidney Stones, trauma, carcinoma
(use the aetiological sieve)
• Ureter Tumours, stones, infection
• Bladder Infection, tumour, stones
• Prostate Benign hypertrophy, tumour,
infection
• Urethra Stone, infection, trauma, etc

11. TISSUE TYPES
• Try to list the causes of a lump in the groin
A good method is to use tissue types, i.e. say that this lump
can arise from any of the tissue types in this region
Tissue type Example
Skin Sebaceous cyst
Adipose tissue Lipoma
Connective tissue Fibroma
Lymphatics Enlarged lymph node
Blood vessels Saphena varix, femoral artery aneurysm
Inguinal canal Inguinal hernia, hydrocoele of the cord
Femoral canal Femoral hernia
Testes Undescended testes

13. “MAGIC ADDITIVE”
M - Metabolic - e.g. gout, hypoglycemia
A- Autoimmune - e.g. lupus, Crohn's disease
G- Genetic - e.g. cystic fibrosis
I - Infective (bacterial, viral, fungal, protozoal,
parasitic) - e.g. gastroenteritis, pneumonia
C- Cancer - e.g. lung cancer, lymphoma

14. A- Acquired (environmental factors) - e.g. COPD,
asbestosis
D - Degenerative - e.g. osteoarthritis, dementia
D- Drugs - e.g. penicillin allergy, Clostridium
difficile infection after antibiotics
I - Insanity - psychiatric conditions e.g. depression,
factitious diarrhea
T- Trauma - gun shot wound, surgical trauma
I - Idiopathic - conditions with unknown cause e.g.
idiopathic intracranial hypertension
V- Vascular - e.g. stroke, angina
E- Endocrine - e.g. diabetes, acromegally

16. “VITAMIN CDEF”
Vascular
Infective/Inflammatory
Traumatic
Autoimmune
Metabolic
Iatrogenic/Idiopathic
Neoplastic
Congenital
Degenerative/Developmental
Endocrine/Environmental
Functional

17. “MIDNITE”
Metabolic,
Inflammation
Degenerative
Neoplastic
Infection
Trauma
Environmental.

18. “INVITED MDC”
Infective,
Neoplasitic
Vascular
Inflammatory/Autoimmune
Trauma
Endocrine
Degenerative
Metabolic
Drugs
Congenital

19. “CA INVITED MD III”
Congenital
Acquired
Infective
Neoplastic
Vascular
Inflammatory
Trauma
Endocrine
Degenerative
Metabolic
Drugs
Idiopathic
Iatrogenic
Immunological

20. “MEDIC HAT PINE”
Metabolic - Fluid & Electrolyte
Imbalance, Hypoglycaemia, Gout
Endocrine - Diabetes, Adrenal disorders, Thyroid
Disorders
Degenerative - Osteoarthritis, Alzheimers Disease
Infective/Inflammatory - Bacterial, Viral, Fungal,
Parasitic,Pneumonia, Gastroenteritis, Meningitis
Congenital - Genetic Conditions, Down Syndrome

21. Haematological - Leukaemia, Stroke, Pulmonary
Embolism, Anaemia
Autoimmune - Systemic Lupus Erythematosus,
Crohn's Disease
Trauma - Fracture, Acute Injury
Psychological/Neurological - Functional disorders,
Depression
Iatrogenic/Idiopathic - Medication & surgically
induced, Poisoning, Allergy
Neoplastic - Primary or Secondary, Paraneoplastic
phenomena
Environmental - conditions relating to exposures, and
dose-response relationships thereof

23. What are the causes of an
acute confusional state in a patient?
Idiopathic/Iatrogenic: polypharmacy, sedatives,
analgesics, steroids, drug withdrawal
Vascular: stroke, TIA, vascular dementia
Inflammatory: infection, systemic inflammatory
response syndrome
Traumatic: head injury, Intracranial hemorrhage, shock
Autoimmune: thyroid disease
Metabolic: electrolyte
imbalance, DKA, hypoglycaemia, SIADH
Infective: sepsis, local infection
Neoplastic: brain tumour, carcinomatosis
Degenerative: Alzheimer's Disease, dementia

24. What are the causes of splenomegaly?
Idiopathic: Idiopathic thrombocytopenic purpura
Vascular: portal vein obstruction, Budd-Chiari
syndrome, haemoglobinopathies(Sickle-cell
disease, thalassemia)
Infective: AIDS, mononucleosis, septicaemia, tuberculosis,
brucellosis, malaria, infective endocarditis
Traumatic: haematoma, rupture
Autoimmune: rheumatoid arthritis, SLE
Metabolic: mucopolysaccharidoses, amyloidosis, Tangier
disease, Gaucher's disease
Inflammatory: sarcoidosis
Neoplastic: CML, metastases, myeloproliferative disorders

25. INVESTIGATIONS
Always break down investigations in the following
manner:
1. Simple urine and faecal tests (e.g. urine dipstix,
microscopy and culture, pregnancy tests, faecal
occult blood)
2. Haematological tests (routine, e.g. FBC, or
special, e.g. tumour markers)
3. Radiological tests (e.g. CXR, ultrasound or CT)
4. Special investigations (e.g. gastroscopy, V/Q
scans)

26. MANAGEMENT
• ‘Discuss the treatment of benign prostatic
hypertrophy’ is a different question from ‘Discuss
the management of benign prostatic
hypertrophy.’
• Management involves discussing all of the steps
that deal with a clinical problem, including the
history, examination, investigations, formation of
a diagnosis and treatment.
• When discussing treatment you can again break
down your answer into subheadings.

27. • For example: treatment can be conservative, medical
or surgical.
• For example, in this case:
 Conservative.
This usually means ruling out cancer. A prostate specific
antigen (PSA) 4 and a normal examination would help
the doctor reassure the patient and a policy of watchful
waiting may be adopted until the symptoms get worse.
 Medical. For example, drugs such as 1-adreno-
receptor blockers or 5--reductase inhibitors.
 Surgical. For example, trans-urethral resection of the
prostate (TURP).

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29. Good Luck
Good Luck With Your Studies