The anomalies of the inferior vena cava (IVC) have an incidence between 0.2 and 1 % in the general population [1]. The normal average diameter of the IVC is 17.5 mm (up to 25 mm maximum) and the spectrum of anatomical abnormalities of the IVC (e.g., absence or interruption of the vessel or variation in diameter) can be responsible for serious hemodynamic effects to the venous circulation of the lower limbs (i.e., venous stasis), and be a risk factor for the development of deep vein thrombosis (DVT). The association between hypoplasia of the IVC (HIVC) and DVT has been previously reported, even though the association of absence of the IVC and DVT is more frequently recorded [2]. Hypoplasia of the inferior vena cava should be taken into account when an unexplained DVT occurs in young patients, as DVT can occur in up to 5 % of young adults with IVC anomalies [3].

A 32-year-old man was referred to our Unit of Internal Medicine because of acute and intense back pain. History was unrevealing for risk factors related to venous disease, but the man had remained immobilised 3–4 days because of the intense pain. After admission, he underwent full (abdominal and pelvic) ultrasound examination, which revealed bilateral proximal (iliac–femoral veins) DVT (Fig. 1a, b; see Fig. 1c for comparison) and severe dilatation of the superficial venous circle of the lower limbs. Laboratory investigations for thrombophilic defects (including factor V Leiden, prothrombin G20210A, mutations A1298C and C8677T, proteins C and S and antithrombin III) were all negative.

Fig. 1
figure 1

Colour assisted (a) and colour assisted compression (b) ultrasound examination of the lower limbs in the reported patient showing deep venous thrombi in the right common femoral vein; normal deep venous vessels in an otherwise healthy 35-year-old patient (c)

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A computed tomography (CT scan) study of the superior abdomen showed hypoplasia of inferior vena cava (diameter 11 × 5 mm) along with bilateral thrombosis of the iliac and hypogastric veins; the right iliac vein was dilated and the paralumbar veins were hypertrophic; dilatation of the right hypogastric venous circle was present (Fig. 2a; see Fig. 2b for comparison).

Fig. 2
figure 2

Axial computerised tomography (CT) scans of the abdomen: a in the reported patient shows hypoplasia of the inferior vena cava and marked dilatation of the paralumbar veins (white arrows), b in a normal vena cava of an otherwise healthy 35 year-old man

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Treatment with subcutaneous low molecular weight heparin was initiated, and shortly followed by oral anticoagulant therapy (INR range 3.0) with application of stocking bandage compression to the lower limbs. Currently, the man is still under follow-up at our unit: his general condition is good with no further recorded episodes of thrombosis; he is still taking oral anticoagulant therapy.

Anomalies of the IVC are a rare finding in clinical practice, but should be suspected when an unexplained DVT presents in a young adult, particularly in the absence of risk factors such as inherited thrombophilia. The main findings in patients with DVT and HICV are summarised in Table 1. Notably, dilatation of the ascending lumbar veins, paravertebral venous plexus, azygous and hemiazygous veins are typical imaging findings of these patients. The hemodynamic data on venous return from the lower part of the body are crucial for differentiating acute and chronic anomalies of the IVC.

Table 1 Common clinical, haemodynamic and imaging findings in patients with DVT and HICV
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Although ultrasonography is useful to demonstrate anomalies of the IVC, by revealing the lack of continuity of the IVC segment and the presence of collateral veins in the abdomen or in the retroperitoneal region, the gold standard of imaging is a CT scan (Fig. 2) or magnetic resonance imaging studies, which are more sensitive and specific in showing the anomalies of the IVC, and to explain the pathophysiology and pathogenic causes underlying the DVT in lower limbs [4, 5].

Despite the increasing availability of such imaging techniques, the recorded cases of DVT and HICV are still limited. The most recent epidemiological data show that the general incidence of DVT (with or without pulmonary embolism) is around 160–182 cases/1,00,000/year [4].

Physicians need to be aware that, especially in a young patient, that if a venous thrombotic disease manifests without an overt cause (i.e. vascular anomalies, hypercoagulability, prolonged stasis) the occurrence of an anomaly of the IVC (e.g., agenesia, atresia, hypoplasia) must be taken into consideration, and that the current imaging techniques can easily detect such anomalies [5].

In young patients, back pain and a history of prolonged immobilisation represents crucial features that suggest the presence of a DVT and IVC. The current imaging tools (e.g., US, CT scan, MRI) are highly sensitive and specific in the diagnostic work-up. Early treatment avoids complications.