RULES IN RADIOLOGY
RULE OF TENS (TEN% TUMOR)
Pheochromocytoma follows it:
10% bilateral/multiple
10% familial
10% malignant
10% extra-adrenal
10 % of insulinoma:
10% are associated with men 1
10% are multiple
10% have islet cell hyperplasia
10% are malignant.
Rule of 10’S
Wilms’ tumor follows it:
• 10% unfavorable histology
• 10% bilateral
• 10% vascular invasion
• 10% calcifications
• 10% pulmonary metastases at presentation.
Rule of Three’s
Spinal cord follows it, above L3 by age 3 months, i.e. spinal
cord should be above L3 vertebrae by age of 3 months.
Rule of 3’s
Small bowel follows it:
• Wall thickness <3 mm
• Valvulae conniventes <3 mm
• Diameter <3 cm
• Air-fluid levels <3.
Rule of 3’s
Hydrostatic/pneumatic reduction follows it:
• Indication: Intussusception
• CID: Peritonitis, pneumoperitoneum, hypovolemic shock.
Procedure
• Patient is sedated
• Anal seal is put with 24-F Foley’s catheter and balloon
inflated; balloon pulled down to levator sling; taped to
buttocks; and both buttocks firmly taped together.
• Air or 60% wt/vol barium sulfate with container between
24-36 inches above level of anus:
– 3.5 feet (105 cm) above table
– 3 attempts max
– 3 minutes between attempts (delay allows venous
congestion and edema to subside).
Rule of 1/3
Carcinoid follows it:
• 1/3 occur in small bowel
• 1/3 have metastases
• 1/3 are multiple
• 1/3 have a second malignancy.
RULE OF 2s
Meckel’s diverticulum follows it:
• This diverticulum is formed due to persistence of the
Vitelline duct, which usually obliterates by 5th embryonic
week
• Common in 2% of population, symptomatic usually
before age of 2 years, located within 2 feet of ileocecal
valve, length of 2 inches.
4712 RULE
It refers to normal splenic measurements:
• Thickness — 4 cm
• A-P diameter— 7 cm
• Length — 11cm
Most commonly used method is:
Eyeball technique, i.e. if it looks big, it is Big.
Rule of Thumb
Crown-rump length (CRL) follows it. It refers to the length
of fetus.
• Menstrual age in weeks = CRL (in cm) + 6
Renal Measurements
As a rule left kidney is usually 2% longer than right kidney.
As a rule, normally:
• Left hilum is at higher level than right hilum
• Right dome of diaphragm is at higher level than left dome
• Left kidney is at higher level than right kidney
• Right testis is at higher level than left testis.
Rule of Eight
Applied in case of delayed contrast excretion by kidneys in
IVU study. For example: If it takes 30 minutes for contrast
to fill the calices, then 4 hours is about right for the next film
and so on (i.e. next film is taken 8 times of first).
Harris Rule of 12s
• This is applied to diagnose atlanto-occipital dislocation
• In this two distances are measured:
– Distance from the base of dens to the clivus
– Distance from a line drawn from the posterior wall of
dens to the clivus.
• Considered abnormal if clivus is >12 mm above the tip of
dens or 12 mm anterior to the posterior dens line.
Ten Days Rule
According to this rule diagnostic X-ray irradiation procedure
involving the pelvic region of females of child bearing age
shall be limited to the 10 days period, following the onset of
last menstruation, in order to prevent irradiation of an
unrecognized early pregnancy.
RULE OF TENS (TEN% TUMOR)
Pheochromocytoma follows it:
10% bilateral/multiple
10% familial
10% malignant
10% extra-adrenal
10 % of insulinoma:
10% are associated with men 1
10% are multiple
10% have islet cell hyperplasia
10% are malignant.
Rule of 10’S
Wilms’ tumor follows it:
• 10% unfavorable histology
• 10% bilateral
• 10% vascular invasion
• 10% calcifications
• 10% pulmonary metastases at presentation.
Rule of Three’s
Spinal cord follows it, above L3 by age 3 months, i.e. spinal
cord should be above L3 vertebrae by age of 3 months.
Rule of 3’s
Small bowel follows it:
• Wall thickness <3 mm
• Valvulae conniventes <3 mm
• Diameter <3 cm
• Air-fluid levels <3.
Rule of 3’s
Hydrostatic/pneumatic reduction follows it:
• Indication: Intussusception
• CID: Peritonitis, pneumoperitoneum, hypovolemic shock.
Procedure
• Patient is sedated
• Anal seal is put with 24-F Foley’s catheter and balloon
inflated; balloon pulled down to levator sling; taped to
buttocks; and both buttocks firmly taped together.
• Air or 60% wt/vol barium sulfate with container between
24-36 inches above level of anus:
– 3.5 feet (105 cm) above table
– 3 attempts max
– 3 minutes between attempts (delay allows venous
congestion and edema to subside).
Rule of 1/3
Carcinoid follows it:
• 1/3 occur in small bowel
• 1/3 have metastases
• 1/3 are multiple
• 1/3 have a second malignancy.
RULE OF 2s
Meckel’s diverticulum follows it:
• This diverticulum is formed due to persistence of the
Vitelline duct, which usually obliterates by 5th embryonic
week
• Common in 2% of population, symptomatic usually
before age of 2 years, located within 2 feet of ileocecal
valve, length of 2 inches.
4712 RULE
It refers to normal splenic measurements:
• Thickness — 4 cm
• A-P diameter— 7 cm
• Length — 11cm
Most commonly used method is:
Eyeball technique, i.e. if it looks big, it is Big.
Rule of Thumb
Crown-rump length (CRL) follows it. It refers to the length
of fetus.
• Menstrual age in weeks = CRL (in cm) + 6
Renal Measurements
As a rule left kidney is usually 2% longer than right kidney.
As a rule, normally:
• Left hilum is at higher level than right hilum
• Right dome of diaphragm is at higher level than left dome
• Left kidney is at higher level than right kidney
• Right testis is at higher level than left testis.
Rule of Eight
Applied in case of delayed contrast excretion by kidneys in
IVU study. For example: If it takes 30 minutes for contrast
to fill the calices, then 4 hours is about right for the next film
and so on (i.e. next film is taken 8 times of first).
Harris Rule of 12s
• This is applied to diagnose atlanto-occipital dislocation
• In this two distances are measured:
– Distance from the base of dens to the clivus
– Distance from a line drawn from the posterior wall of
dens to the clivus.
• Considered abnormal if clivus is >12 mm above the tip of
dens or 12 mm anterior to the posterior dens line.
Ten Days Rule
According to this rule diagnostic X-ray irradiation procedure
involving the pelvic region of females of child bearing age
shall be limited to the 10 days period, following the onset of
last menstruation, in order to prevent irradiation of an
unrecognized early pregnancy.