Cases & Commentaries

"Superficial" Report Leads to "Deep" Problem

Commentary By Gurpreet Dhaliwal, MD

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.

Term Semantic Issue
Superficial femoral vein • not a superficial vein
Mycotic aneurysm • not due to fungal infection
Lupus anticoagulant • associated with thrombosis (not
anticoagulation) in vivo
Bioprosthetic valve • contains "prosthetic," which may be
confused with a mechanical valve and therefore errantly imply the
need for anticoagulation
Aplastic anemia • pancytopenia, not only red cells
Renal adenoma • synonym for renal cell carcinoma, although
"adenoma" usually connotes benignity
Preoperative clearance • "clearance" implies certainty in
assessment, which is rarely the case
Biliary colic • pain is steady, not colicky
Pretibial myxedema • seen in the opposite condition of
myxedema, i.e., Graves' hyperthyroidism

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.)