The Case

A 35-year-old woman presented to the emergency department (ED) complaining of left foot and ankle pain for the past 7 days. The patient denied any recent trauma to her leg and had no fever or respiratory symptoms. She had no other medical history, and her only medication was an oral contraceptive. She reported smoking one pack of cigarettes daily and drinking alcohol occasionally, but denied illicit drug use. The patient's mother had a history of a "blood clot," but there was no other significant family history.

The physical examination was significant for moderate pitting edema, mild erythema, and tenderness of the left leg from the foot up to the mid-calf area. The left calf circumference was 4 cm greater than the right calf, but there were no dilated superficial veins or palpable venous cords. The patient was able to bear weight on the affected leg but had an antalgic gait (a limp adopted to avoid pain on weight-bearing structures, characterized by a very short stance phase).

The patient had a normal radiograph of her left foot and ankle. The emergency medicine resident evaluating the patient was concerned about the possibility of a deep venous thrombosis and ordered a Doppler ultrasound examination of the left lower extremity. The preliminary radiology interpretation faxed to the ED read, "thrombus left distal superficial femoral vein." The emergency medicine resident and attending physician caring for this patient interpreted this result as representing a superficial vein thrombus. Knowing that superficial venous thromboses can usually be treated safely without anticoagulation (because of their very low risk of causing pulmonary embolism), they diagnosed the patient with cellulitis complicated by a superficial thrombophlebitis and prescribed oral antibiotics along with elevation and warm compresses to the affected leg.

The final report of the patient's ultrasound, which returned many hours later, read, "deep vein thrombosis of the left distal superficial femoral vein." This final interpretation was not communicated to the patient's caregivers. The resident followed up 2 days later on the final reading of the study and recognized that the new information meant that the patient should have been anticoagulated. The patient was contacted and asked to return to the ED for initiation of treatment with low-molecular-weight heparin and warfarin. The patient returned promptly and was treated without any complications. She completed 3 months of therapy, and a follow-up ultrasound showed resolution of her deep vein thrombosis.

The Commentary

The clinicians appropriately considered deep venous thrombosis (DVT) in a 35-year-old smoker taking oral contraceptives with a family history of thrombosis and asymmetric lower extremity edema and pain, and they ordered the appropriate test, but the action they took based on the results was errant. At least two interpretations are possible: the clinicians were unaware that the superficial femoral vein (SFV) is a deep vein and it was only the explicit label of "DVT" on the final report that informed them (knowledge deficit), or they were familiar with the anatomy but committed a cognitive slip in the "heat of battle," which they readily recognized 2 days later (faulty synthesis). Studies suggest that errant information processing, not inadequate knowledge or faulty data collection, is the principal contributor to diagnostic error, but after-the-fact categorization is often ambiguous, as in this case.(1,2)

Whether the clinicians were unaware or forgot that the SFV is a deep vein, they certainly were not alone. In a 1995 study in which clinicians were presented with the scenario of an "occluding [acute] thrombus of the distal superficial femoral vein," only 24% advised anticoagulation, with the remainder choosing nonsteroidal antiinflammatory drugs (NSAIDs) and conservative treatment or re-evaluation in 3 days.(3) An analogous 1996 survey also found that 26% of internists presented with a thrombosis of the SFV advised anticoagulation.(4) Ask any vascular surgeon, radiologist, or hematologist, and you will learn that this error happens repeatedly. How do family practitioners, internists, and emergency medicine physicians consistently overlook the most common DVT site?(5)

Virtually no one learns the term superficial femoral vein during basic anatomy instruction in medical school. The femoral vein (FV) is the preferred term among anatomists (92 of 95 surveyed in one study [3]) for the venous segment that runs between the popliteal vein and the inflow of the deep femoral vein. Accordingly, this terminology is taught in most medical schools (>90% [3]) (Figure). I checked three of my own anatomy textbooks and found only FV, with no mention of the SFV. Official compendia, like Terminologica Anatomica, endorse FV as the preferred term.

Despite this standard among anatomists, most vascular clinicians (surgeons, radiologists, vascular laboratory technicians) adopt the term SFV to clearly distinguish this venous segment from both the deep femoral vein and the common femoral vein.(3) For these specialists (many of whom visualize the vascular anatomy on a daily basis), there is no misconception that the SFV, the principal vein of the thigh (which travels with the superficial femoral artery), is anywhere near the skin. For them, "superficial" is a clarifying, not confusing, modifier.

However, the broad spectrum of clinicians who treat venous thrombosis in emergency, internal, and family medicine have limited daily interaction with this anatomy. From on-the-job experience and interactions with vascular clinicians and reports, they must re-learn the FV, which is understood to be a deep vein, as the SFV. Then the potential confusion induced by the shared adjective in superficial venous thrombosis and SFV requires memorizing a rule: every time you hear SFV, ignore the natural default (this "superficial" vein is not superficial) and remember that it is a deep vein. Anything that saps your cognitive energy—busy clinic or ED, fatigue, diverted attention—at the moment a report is received and the treatment decision is made can derail this corrective strategy.

Solutions

Perhaps the weakest solution to this problem would be to initiate pre- or postgraduate efforts to educate clinicians about this singular aspect of the lower extremity vascular anatomy. The durability of this method is suspect because it relies on human memory, and the confusing nomenclature would still require adoption of the mental rule outlined above.

In this case, the DVT label in the final report either triggered recognition or generated new knowledge leading to appropriate management. A universal requirement that all lower extremity venous Doppler studies explicitly report thromboses as being in the deep or superficial venous system could provide clarity for frontline physicians who are sifting through massive amounts of data in real time. The success of this policy, however, relies on the radiologist's memory (unless a forcing function is introduced like a check box for "DVT" or "no DVT" before release of preliminary readings), and it still presents an opportunity for misinterpretation when the receiving physician sees or hears the word "superficial" intermingled among the reported information.(6)

As long as "superficial" remains in the name, there will always be individual- and systems-level issues that facilitate triggering of the superficial vein thrombosis illness script (which includes no anticoagulation). The most durable fix for this failure of the human mind will likely be a widespread revision of the clinical anatomic terminology that underlies the confusion.

With increased awareness of this common and dangerous error, many vascular laboratories and radiologists have already stopped using the term SFV. Many physicians have called for abandoning the term SFV in favor of FV (3,4,7,8), and an international committee on modern vascular anatomy has endorsed this change.(9) Yet the chasm between the consensus guidelines (put in place by early adopters) and the everyday habits of clinicians is substantial.

The call to drop "superficial" from the name of the vessel where most DVTs occur (5) amounts to a request for one group of physicians (vascular clinicians) to forgo a preferred and well-established terminology for the sake of another, larger group of clinicians who consume and act upon the terminology (and this is not the only confusing and potentially dangerous term in medicine—see Table for others). Language is sustained or changed by those who use it daily; the latter requires a conviction and commitment among those who influence the word choice of others, such as authors, editors, teachers, and consultants. In the case of SFV, the period of change will be marked in years, and the transition may bring about confusion and unexpected consequences, but the effort holds the promise of ensuring proper treatment for tens of thousands of patients each year who currently endure morbidity and mortality (8) because of this predictable and persistent error grounded in nomenclature.

Take-Home Points

• Diagnostic errors can be challenging to categorize as errors of knowledge or cognition, although recent data suggest that errors of cognition are more prevalent.
• Clarification and revision of confusing medical terminology (see Table) have the potential to reduce error.
• The superficial femoral vein is actually a deep vein of the lower extremity; anticoagulation is required in the event of thrombosis.

Gurpreet Dhaliwal, MD Assistant Clinical Professor of Medicine

University of California, San Francisco

San Francisco VA Medical Center

References

1. Graber ML, Franklin N, Gordon R. Diagnostic error in internal medicine. Arch Intern Med. 2005;165:1493-1499. [go to PubMed]

2. Schiff GD, Kim S, Abrams R, et al. Diagnosing diagnosis errors: lesson from a multi-institutional collaborative project. Advances in Patient Safety, Volume 2. 2005;2:255-278. [Available at]

3. Bundens WP, Bergan JJ, Halasz NA, Murray J, Drehobl M. The superficial femoral vein. A potentially lethal misnomer. JAMA. 1995;274:1296-1298. [go to PubMed]

4. Riancho JA, Ontañón A. The superficial femoral vein: a cause of therapeutic error. Lancet. 1996;348:1670. [go to PubMed]

5. Maki DD, Kumar N, Nguyen B, Langer JE, Miller WT Jr, Gefter WB. Distribution of thrombi in acute lower extremity deep venous thrombosis: implications for sonography and CT and MR venography. AJR Am J Roentgenol. 2000;175:1299-1301. [go to PubMed]

6. Schreiber R. Superficial femoral vein thrombosis: a potentially confusing term. JAMA. 1996;275:445. [go to PubMed]

7. Hammond I. The superficial femoral vein. Radiology. 2003;229:604-606. [Available at]

8. Weiss MA, Weiss MM. Superficial thinking. AJR Am J Roentgenol. 2008;190:W318. [Available at]

9. Caggiati A, Bergan JJ, Gloviczki P, Jantet G, Wendell-Smith CP, Partsch H; International Interdisciplinary Consensus Committee on Venous Anatomical Terminology. Nomenclature of the veins of the lower limbs: an international interdisciplinary consensus statement. J Vasc Surg. 2002;36:416-422. [go to PubMed]

Table

Table. Medical Terms with Potential for Morbidity If Misunderstood.

Figure

Figure. Three nomenclatures in use for the deep veins of the thigh. Nomenclature A is the textbook terminology preferred by anatomists. Nomenclature B is not officially recognized but is used by a minority of clinicians. As in the presented case, nomenclature C is commonly used in clinical medicine and may mistakenly cause clinicians to assume that the "superficial femoral vein" is superficial, not deep. (Illustration by Chris Gralapp.)