**6. Additional findings**

194 Pulmonary Embolism

be used alone for suspected PE but could replace angiography in combined strategies that include ultrasonography and lung scanning". Likewise, van Strijen et al. found in a multicentre prospective study that sensitivity of CT was 69% while specificity was 84% and "concluded that the overall sensitivity of spiral CT is too low to endorse its use as the sole test to exclude PE" and that "this holds true even if one limits the discussion to patients with larger PE in segmental or larger pulmonary artery branches" (Van Strijen et al., 2005). Our experience supports this view. Also, CT as a second procedure following scintigraphy has limited value (van Strijen et al., 2003). Multislice CT seems to improve resolution but

A problem associated with limited sensitivity of CT and incomplete coverage of the total lung is that the degree of embolism and lung function deficiency cannot be quantified.

In spite of excellent diagnostic qualities of V/P SPECT and documented low sensitivity of CT, the latter method is often recommended. A high number of non-diagnostic scintigraphies were reported in the PIOPED study (65%) (1990). This is still used as an argument against lung scintigraphy. In PIOPED, scintigraphy was performed with inferior technique and inflexible sub-optimal interpretation criteria. Even with planar scintigraphy, a reduction in the number of non-diagnostic reports to 10% can be achieved with adequate acquisition and a holistic interpretation strategy (Bajc et al., 2002a). With V/P SPECT, this number is further reduced to between 1 and 4%, as found in several studies (Bajc et al., 2008;

Some practitioners hold that sub-segmental emboli are of little importance for otherwise healthy people and may be left untreated and, as a consequence, are prepared to accept less sensitive methods for PE diagnosis. However, small emboli are important because they 1) may be a first and only sign of silent deep venous thrombosis, 2) may precede larger emboli 3) if not diagnosed and/or untreated, further episodes may lead to chronic PE and pulmonary hypertension (Fig. 6). 4) form a threat to patients with limited cardio-pulmonary reserve, 5) are clinically essential for quantification, which is necessary to scientifically establish appropriate treatment protocols. Thus, each embolus is relevant, irrespective of size. Sub-segmental emboli should not be left untreated without further scientific evidence.

Management of PE was previously confined to in-hospital therapy, using anticoagulation,

About 20 % to 55 % of patients with deep venous thrombosis have concomitant PE, which is usually not diagnosed because symptoms of PE are absent. Outpatient treatment of patients with deep venous thrombosis, which is perceived as a safe routine, implies that many patients with PE are treated at home. Home treatment of patients with diagnosed PE has been suggested (Kovacs et al., 2000) but in order to determine the appropriateness of the treatment on an individual basis, the extension of PE obviously need to be estimated. Whilst patients with limited extension of PE may be treated at home, intermediate cases and patients with co-morbidity may need in-hospital treatment. Those with very extensive PE

Obviously, quantification requires studies of the whole lung with methods allowing identification of large and small emboli. V/P SPECT is the ideal method for this purpose as segmental and sub-segmental emboli can be both detected with a high degree of sensitivity

heparin injections followed by oral anticoagulants for extended periods of time.

may require thrombolysis, necessitating inpatient treatment.

sensitivity for small PE appears not to be improved (Stein et al., 2006).

Quantification is important for treatment selection.

Leblanc et al., 2007; Lemb & Pohlabeln, 2001).

**5. Selection of therapeutic strategy** 

PE is a condition known for its non-specific symptoms. Medical imaging, such as V/P SPECT, is therefore necessary to confirm or exclude the diagnosis among patients with suspected PE. The majority of patients that are examined with V/P SPECT, due to the initial assumption of PE, will not have PE. It is therefore important that any alternative diagnoses, which could explain the patients' symptoms, are identified and provided to the referring physician. Possible alternative diagnoses include pneumonia, heart failure, pleural fluid, malignancy and chronic obstructive pulmonary disease (COPD) (Richman et al., 2004). Another important aspect is that these conditions sometimes coexist and that they also elevate the risk of PE (Elliott et al., 2000). V/P SPECT can be employed to identify other diagnoses than PE.
