An Incidental Detection of Popliteal Vein Aneurysm during Labeled Leukocyte Scintigraphy.

Technetium (99mTc) exametazime (hexamethylpropyleneamine oxime, HMPAO) labeled leukocyte scintigraphy is mainly used to exclude occult infection in our institution. On review of previously published article, no case of popliteal venous aneurysm was ever diagnosed and detected on labeled leukocyte scintigraphy. We present a rare case of popliteal venous aneurysm which was detected on labeled leukocyte scintigraphy and was further confirmed with single-photon emission computed tomography and computed tomography fusion.

Introduction

Popliteal vein aneurysm is an uncommon condition. Early diagnosis is important due to the risk of pulmonary embolism. In current practice, the diagnosis is usually made using Doppler ultrasonography of the lower limb. Occasionally, further confirmation and severity assessment of the disease are made using computed tomography or magnetic resonance imaging. Prior to ultrasonography, phlebography was the modality of choice in diagnosing and assessing popliteal vein aneurysm. Popliteal vein aneurysm in an asymptomatic patient was usually an incidental finding at a Doppler scan of the lower limb for other indications such as venous insufficiency or venous thrombosis. We are presenting a case of popliteal vein aneurysm which was detected during a technetium (99mTc) exametazime (hexamethylpropyleneamine oxime, HMPAO) labeled leukocyte scintigraphy for occult infection.

Case Report

Mr. E. K. P was a 77-year-old Chinese gentleman who presented to our institution with 3 days history of fever associated with chills and rigors. There were no other constitutional symptoms. Prior to the current admission, he was treated for a liver abscess which had resolved. The patient's past medical history included tablet-controlled Type 1 diabetes mellitus, a previous cholecystectomy, and a previous repair of a perforated peptic ulcer.

On examination, he was found to be afebrile with stable vital signs. There were bilateral basal lung crepitations on auscultation. The rest of the systemic examination was unremarkable. Blood investigation showed elevated glucose level of 18.2 mmol/l. Full blood count revealed leukocytosis with total count of 23.7 × 109/l and mild thrombocytopenia with a platelet count of 139 × 109/l. Liver function test showed mild elevation of alkaline phosphatase and γ-glutaryl transaminase.

A supine chest radiograph was performed on admission which was also unremarkable. Ultrasound of the hepatobiliary system was performed on admission to exclude recurrent liver abscesses, which also turned out to be negative.

The patient was admitted for blood glucose control and antibiotic treatment. Repeat physical examination in the ward revealed bronchial breathing in the right lower zone with crepitations and signs of a right pleural effusion which was confirmed on a right decubitus chest radiograph. He was then treated for community-acquired pneumonia and was started on intravenous Imipenem (Tienem®). Patient responded clinically well initially to the treatment.

However, despite treatment, C-reactive protein and erythrocyte sedimentation rate (ESR) levels remained elevated at 17.1 mg/dl and 75 mm/h, respectively. A leukocyte labeled scintigraphy was then performed to exclude other foci of infection, which turned out to be negative except for an intense tracer uptake in the left distal thigh. A fused single-photon emitter computed tomography and computed tomography (SPECT-CT) was performed, and a diagnosis of a left popliteal vein aneurysm was made. No evidence of thrombosis was noted.

Discussion

A venous aneurysm is a rare condition. Schild et al. had collated 311 cases of venous aneurysms reported in the literature from 1939 to 1992.[1] The most frequently involved vessels were the internal jugular and saphenous veins. Symptoms depended on the site of the aneurysms and were mainly non-specific. 62% of patients were below 40 years of age and pulmonary embolisms were only seen in 19 out of 311 patients, accounting for 6.1%.

Subsequent studies of popliteal vein aneurysms had shown predilection toward the female population of above 40 years of age, to which the etiology remains unknown. Sessa et al., in a retrospective analysis of management of symptomatic and asymptomatic popliteal venous aneurysms in 25 patients, discovered that six patients (24%) developed pulmonary embolism.[2] Four out of these six patients had thrombus within the aneurysm which was diagnosed by ultrasound examination, thus stressing the importance of early treatment of the aneurysm with the presence of thrombus within. The rise in the proportion of the patients with pulmonary embolism having popliteal vein aneurysm is probably due to wide use of Doppler ultrasonography in excluding deep venous thrombosis as the cause.

Diagnosis and management of popliteal vein aneurysm are important in view of its life-threatening complications, mainly from pulmonary embolism. The treatment of symptomatic popliteal vein aneurysm is surgery, while for the asymptomatic patients it remains controversial.[2] Color Doppler ultrasonography is the preferred non-invasive diagnostic tool in current practice due to its wide availability.[3] It allows measurement of the aneurysm as well as assessment of its morphology and detecting the presence of thrombus within. Color Doppler ultrasonography is used in follow-ups to assess the size and formation of thrombus.

Positive labeled leukocyte scintigraphy is determined by increased focal tracer accumulation. False-positive results have been reported in acute bleed, hematoma, intravenous line localization, localized bile collection, and neoplasms, among other things.[4] There has been no reported case of a venous aneurysm as the cause of a false-positive result in labeled leukocyte scintigraphy.

In our patient, the striking feature was the focal increase in tracer uptake at the left knee during the venous pool phase [Figure 1]. As the patient did not reveal any symptoms or signs of inflammation around the left knee during the interview prior to the study, a SPECT–CT was performed for the left knee to localize the region of the tracer uptake. There was a fusiform aneurysm of the left popliteal vein showing high tracer activity [Figure 2]. Fusiform aneurysm of the popliteal vein is less common compared to the saccular type, accounting for 25% of the patients.[5]

Figure 1

Tc-99m leukocyte scan of the lower extremity. Posterior view showing an abnormal intense focus of increased radio tracer uptake in the region of left popliteal fossa along the popliteal vessel

Figure 2

SPECT–CT fusion image of the popliteal region showing localization of this focal uptake in the fusiform aneurysm of the left popliteal vein

Due to wide diameter of the aneurysm, the blood flow through the aneurysm is slow compared to the rest of the venous system. We postulate that the slow flow or focal stasis within the aneurysm may be the cause of the localized tracer accumulation observed in our patient's study. For future reference, when a localized tracer accumulation in the perivascular region is seen on a white blood cell (WBC) tagged technetium 99m HMPAO study, a venous aneurysm needs to be considered, hence the need for SPECT/SPECT–CT to further localize the site.