In an adult patient with an unprovoked pulmonary embolism, should a CT abdomen be performed to screen for occult cancer?

CT Abdomen for Unprovoked PE: Not Routinely Recommended

Routine CT abdomen/pelvis should NOT be performed for occult cancer screening in patients with unprovoked pulmonary embolism. Instead, pursue limited cancer screening with thorough history, physical examination, basic laboratory tests, chest X-ray, and age/gender-appropriate cancer screening only 1.

Evidence Against Routine CT Abdomen

The International Society on Thrombosis and Haemostasis (ISTH) guidance explicitly recommends against extensive screening strategies, including CT abdomen/pelvis, for first unprovoked VTE 1. Here's why:

Key Evidence Points

• No improvement in cancer detection rates: Multiple prospective studies comparing extensive screening (including CT abdomen/pelvis) versus limited screening showed that extensive strategies did not detect more occult cancers than limited approaches 1

• No proven mortality benefit: While extensive screening may detect earlier-stage tumors, there is no evidence this translates into improved patient survival or decreased morbidity 1

• Not cost-effective: Cost-utility analysis demonstrated that extensive screening including CT abdomen/pelvis is not cost-effective 1

• Potential harms: Aggressive screening carries significant psychological burden, economic costs, and may lead to premature anticoagulation withdrawal (risking recurrent VTE) 1

What You SHOULD Do Instead

Recommended limited screening approach 1:

• Thorough medical history and physical examination - looking specifically for constitutional symptoms (unexplained weight loss, night sweats), bleeding, masses, lymphadenopathy 1

• Basic laboratory investigations 1:

  • Complete blood count
  • Calcium level
  • Urinalysis
  • Liver function tests

• Chest X-ray 1

• Age-appropriate and gender-specific cancer screening per national guidelines 1:

  • Colonoscopy (age-appropriate)
  • Mammography (women)
  • Cervical cancer screening (women)
  • Prostate cancer screening (men, if indicated)

Important Caveats and Exceptions

Consider Lower Threshold for Extensive Screening In:

• Recurrent unprovoked VTE: 17% of these patients develop cancer within 2 years versus 4.5% with single VTE (OR 4.3) 1. A lower threshold for additional imaging may be reasonable 1

• High-risk features per NICE guidance 1:

  • Bilateral deep vein thrombosis
  • Very high D-dimer levels
  • Early VTE recurrence

Special Situations Where CT Abdomen IS Indicated:

• Splanchnic vein thrombosis: CT abdomen/pelvis is the diagnostic modality for the thrombosis itself and simultaneously screens for gastrointestinal, pancreatic, or hepatobiliary malignancies (present in up to 30% of cases) 1

Divergent Guidelines: Why the Controversy?

There is genuine disagreement in the literature:

• UK NICE guidelines (based on data through 2012) suggest CT abdomen/pelvis may provide more benefit than harm in patients >40 years with unprovoked VTE 1

• ISTH and Anticoagulation Forum (more recent, 2017) recommend against routine extensive screening 1

The ISTH guidance should take precedence as it represents the most recent consensus (2017) and explicitly addresses the lack of mortality/morbidity benefit, which is your priority outcome 1.

Clinical Pitfalls to Avoid

• Don't order unnecessary D-dimer tests after PE is already diagnosed - this doesn't guide cancer screening decisions 1

• Don't use unvalidated risk prediction rules for deciding on extensive screening - none have been validated for clinical use 1

• Don't forget the 5% occult cancer rate in unprovoked VTE represents a 4-6 fold increased risk versus general population, but this doesn't justify indiscriminate imaging 1

• Remember cancer risk remains elevated for up to 6 years for certain malignancies (colon, pancreatic, multiple myeloma), so maintain clinical vigilance during follow-up 1