Teaching Case

59-year-old woman referred from screening. Negative personal and family history.

Screening mammography shows heterogeneous dense breasts and an architectural distortion centrally in the right breast as well as a circumscribed mass with macro- and microcalcifications (most likely a fibroadenoma) craniolaterally (Fig. 1).

Ultrasound demonstrates an irregular, hypoechoic, spiculated mass with posterior shadowing and no vascularisation on Doppler (Fig. 2). Ultrasound of the right axilla shows a large, inhomogeneously hypoechoic mass adjacent to the axillary vessels without internal vascularisation in Doppler. The mass is oval to fusiform and shows (at least partially) an echogenic capsule (Fig. 3).

An 18F-FDG PET/MRI examination confirms the spiculated, T2-W hypointense mass with surrounding oedema, early intense enhancement and a wash-out in the late phase (Fig. 4). The mass is FDG-avid (SUVmax: 3,5) (Fig. 5). In the right axilla, several circumscribed lesions are evident. They are hypointense in T1-WI (Fig. 6) and hyperintense in PD-WI with fat-suppression (Fig. 7).  In T2-WI they are inhomogeneously hyperintense with hypointense areas (Fig. 8). They demonstrate moderate, heterogeneous contrast enhancement (Fig. 9) and moderate FDG-avidity (SUVmax: 1,7) (Fig. 10).

Background

Neurofibromas are, along with schwannomas, the most usual peripheral benign nerve sheath tumours, usually found in young adults. They originate from Schwann cells of the nervous sheath but also include non-neoplastic components [1]. Although they usually occur sporadically, they are sometimes part of neurofibromatosis 1.

Clinical Perspective

Symptoms usually include pain, palpable masses and motor/sensory deficits [2,3]. In a breast cancer patient, metastatic axillary lymph nodes need to be excluded. Although preoperative diagnosis may be challenging, it is essential for the appropriate patient management.

Imaging Perspective

On US neurofibromas usually present as circumscribed, fusiform, hypoechoic masses with hyperechoic foci due to collagen deposits. They may have an echogenic capsule and are usually hypovascular on Doppler [4,5]. Metastatic lymph nodes, however, present a thickening of the cortex and a fatty hilum. If they are completely infiltrated, the hilum is not seen and they become rounded and hypoechoic. They are usually hypervascular and often have non-hilar cortical flow on Doppler [6].

On MRI neurofibromas are circumscribed, hypo- to isointense in T1-WI and homogeneously or heterogeneously hyperintense in T2-WI. A central T2 hypointensity (“target-sign”) is attributed to dense collagen, whereas the peripheral hyperintensity to myxoid tissue [7]. In contrast-enhanced T1-WI they usually show intense enhancement [3,7]. Metastatic lymph nodes are usually asymmetric, either rounded or with a focal cortical thickening and sometimes surrounding oedema [6].

On 18F-FDG PET neurofibromas are usually hypermetabolic, with lower SUVmax values than malignancies [8].

If histologic verification is necessary, US-guided biopsy may be performed. However, this is usually painful for the patient and may have to be interrupted [5]. This also happened with our patient.

Outcome

Neurofibromas are usually treated conservatively; however, resection may be necessary for symptomatic, rapidly growing tumours with a possibility of malignancy [9]. Since surgery depends mainly on the lesion’s anatomic location, imaging (especially MRI) is necessary to provide regional anatomic details. If complete resection is possible, results are usually very good. In selected cases, if complete resection is difficult, radiotherapy is indicated [10].

Take Home Message / Teaching Points

1. Axillary neurofibromas can mimic metastatic lymph nodes.

2. Imaging findings on US and especially on MRI help pose the correct diagnosis.

3. Since axillary status is crucial for breast cancer staging, US-guided biopsy may be necessary. However, puncture of neurofibromas (in contrast to lymph nodes) can be very painful, something that can also indicate the correct diagnosis.