Radiology Reference Values

The following is a list of common measurement value normal ranges for various radiology studies.

Head / Neck
  • A line drawn between the lateral orbital margins should cross the posterior third of the globes. 
  • Atlantodental interval: < 3 mm adults; < 5 mm children
  • Prevertebral soft tissue thickness: < 7 mm at C2; < 2 cm at C7

Chest
  • Azygos vein: < 10 mm
  • Paratracheal stripe: < 5 mm
  • Recommendations for Follow-up and Management of Indeterminate Lung Nodules Detected Incidentally on Nonscreening CT
    • Low-Risk Patient:
      • Nodule Size = 4 mm: No follow-up needed.
      • Nodule Size > 4 - 6 mm: Follow-up at 12 months. If no change, no further imaging needed.
      • Nodule Size > 6 - 8 mm: Initial follow-up CT at 6 -12 months and then at 18 - 24 months if no change.
      • Nodule Size > 8 mm: Follow-up CTs at 3, 9, and 24 months. Dynamic contrast enhanced CT, PET, and/or biopsy
    • High-Risk Patient:
      • Nodule Size = 4 mm: Follow-up at 12 months. If no change, no further imaging needed.
      • Nodule Size > 4 - 6 mm: Initial follow-up CT at 6 -12 months and then at 18 - 24 months if no change.
      • Nodule Size > 6 - 8 mm: Initial follow-up CT at 3 - 6 months and then at 9 -12 and 24 months if no change.
      • Nodule Size > 8 mm: Same at for low risk patients
    • Notes: diameter = average width; high risk is defined as a history of smoking or other know risk factors for lung cancer; low risk is defined as minimal or absent history of smoking or other known risk factors; caveat: nodules with a ground glass component may require longer follow up to exclude indolent adenocarcinoma.
  • Adapted from the Fleischner Society Statement on CT of Small Pulmonary Nodules (Radiology 2005;237:395-400)
  • Recommendations for the Management of Subsolid Pulmonary Nodules Detected at CT: A Statement from the Fleischner Society
    • Solitary pure Ground Glass Nodule (GGN)
      • ≤ 5 mm: No CT follow-up required
      • >5 mm: Initial follow-up CT at 3 months to confirm persistence then annual surveillance CT for a minimum of 3 years
      • Solitary part solid nodule: Initial follow-up CT at 3 months to confirm persistence. If persistent and solid component ≤5 mm, then yearly surveillance CT for a minimum of 3 years. If persistent and solid component >5 mm, then biopsy or surgical resection
    • Multiple subsolid nodules
      • Pure GGNs ≤ 5 mm: Obtain follow-up CT at 2 and 4 years
      • Pure GGNs >5 mm without a dominant lesion(s): Initial follow-up CT at 3 months to confirm persistence and then annual surveillance CT for a minimum of 3 years
      • Dominant nodule(s) with part-solid or solid component Initial follow-up CT at 3 months to confirm persistence. If persistent, biopsy or surgical resection is recommended, especially for lesions with >5 mm solid component
    • Reference: Recommendations for the Management of Subsolid Pulmonary Nodules


Abdomen
  • Aorta < 3 cm
  • Liver: < 15 cm in mid-axillary line
  • Gallbladder wall: < 3 mm
  • Common bile duct: < 7 mm
    • Post cholecystectomy: < 10 mm
  • Pancreatic duct
    • Head: < 3.5 mm
    • Body: < 2.5 mm
    • Tail: < 1.5 mm
  • Spleen: < 13 cm
  • Appendix < 6 mm; 6-7mm gray zone
  • Small bowel: < 3 cm diameter
  • Cecum: < 9 cm 
  • Transverse colon: < 6 cm


Pelvis

OB

- Findings diagnostic of pregnancy failure:
  •  Crown-rump length of ≥ 7 mm and no heartbeat 
  • Mean sac diameter of ≥ 25 mm and no embryo 
  • Absence of embryo with heartbeat ≥ 2 weeks after a scan that showed a gestational sac without a yolk sac 
  • Absence of embryo with heartbeat ≥ 11 days after a scan that showed a gestational sac with a yolk sac 
- Findings suspicious for but not diagnostic of pregnancy failure:
  • Crown-rump length of < 7 mm and no heartbeat 
  • Mean sac diameter of 16-24 mm and no embryo 
  • Absence of embryo with heartbeat 7-13 days after a scan that showed a gestational sac without a yolk sac 
  • Absence of embryo with heartbeat 7-10 days after a scan that showed a gestational sac with a yolk sac 
  • Absence of embryo ≥ 6 weeks after last menstrual period 
  • Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo) 
  • Enlarged yolk sac (>7 mm) 
  • Small gestational sac in relation to the size of the embryo (< 5 mm difference between mean sac diameter and crown-rump length)
  • A subchorionic hemorrhage is considered small if it is <20% of the gestational sac; large if >50-66% of the gestational sac.

MSK
  • Positive ulnar variance: Ulnar tip extending 2.5 mm past the radius at the distal radio-ulnar joint. 
    • Associated with ulnar impaction syndrome.
  • Negative ulnar variance: Ulnar tip 2.5 mm or shorter than the radius at the DRUJ
    • Associated with Kienbock malacia and ulnar impingement syndrome
  • Boehler's angle: 20-40 degrees