Teaching Case

An eight-year-old girl has many cats at home and she usually plays with them. That is why she presented scratches mainly in her arms and forearms. She had fever and pain in the medial part of the left elbow. The mass appeared 3 weeks ago.

5cm above the left humeral epitrochlea there is an elongated structure, with fusiform morphology and well delimited borders corresponding to an adenopathy. It presents a lobular cortical thickening mainly of the inferior pole (Fig. 1). Colour-Doppler study shows a homogeneous hilar hyperaemia (Figure 2).

T1-weighted (Fig. 3), T2-weighted (Fig. 4), T1-weighted gadolinium enhanced, fat-saturated (Fig. 5) and PDWI (Fig. 6) show a corresponding well-defined soft tissue mass (arrows) that enhances homogeneously and presents inflammatory changes in the surrounding subcutaneous tissue. The markedly hypoechoic images suggestive of necrotic foci visualised on ultrasound are not displayed, suspectedly because it is not yet an evolved process.
There is no evidence of dependence on muscular, vascular or nerve structures. There were no associated collections.

Cat-scratch disease (CSD, also known as cat-scratch fever or subacute regional lymphadenitis) is typically a self-limiting infectious condition, often presenting in children and adolescents as a benign regional lymphadenitis that results from a cat scratch or bite involving the distal upper extremity [3]. Bartonella henselae, a gram-negative rod, is considered the principal aetiologic agent.
The development of a palpable mass may raise clinical concern for a soft tissue neoplasm, such as sarcoma, lymphoma, or metastatic disease; therefore, imaging evaluation
is often considered.

The hallmark of cat-scratch disease is painful lymphadenopathy proximal to the site of inoculation.
When a lymph node is enlarged but maintains an oval shape, normal echogenic hilum, and hilar hypervascular pattern, then hyperplasia from inflammation is suggested. One such example is CSD, in which the scratch of a cat characteristically produces epitrochlear lymph node enlargement [5, 2, 3]. Lobular cortical thickening may be present, focal or diffuse, but this is not a specific finding of CSD. As such, when this finding is present, one should also consider alternative diagnoses [5].
These lymph nodes may be multiple and contiguous, and tend to develop central necrosis and liquefaction over time. The hyperechogenic infiltration of periganglionar fat due to cellulitis is also a typical finding, although not always present [1].
Sometimes, a lymph node shows enlargement associated with extensive stranding of the surrounding soft tissues. These findings are non-specific, nonetheless suggestive of an inflammatory process such as any bacterial, fungal, granulomatous, or parasitic infection.
In the appropriate clinical setting, a lymph node enlargement with stranding and only mild oedema of the surrounding soft tissues as demonstrated by MR imaging may be diagnostic of cat-scratch disease.
It is important to note that these findings can be adequately demonstrated without utilising gadolinium-DTPA enhancement; however, enhancement may be helpful in delineating areas of necrosis [3].

Lymph node biopsy generally is not indicated in typical cases of CSD, given the associated morbidity. Node aspiration in patients suspected of having CSD traditionally has been discouraged for fear of fistula formation. Ultrasonography may be performed to determine if a lymph node is fluctuant and amenable to needle aspiration [4].
In this case, serology was positive for B. henselae.

Other manifestations of CSD: Encephalopathy, neuroretinitis, osteomyelitis, Parinaud's syndrome (granulomatous conjunctivitis with adenopathy), among others.
Treatment: For most patients with mild or moderate CSD, only conservative symptomatic treatment is recommended because the disease is self-limited. In some cases, treatment with antibiotics such as azithromycin can be helpful.