Multiple localised and plexiform neurofibromas due to neurofibromatosis type 1

A 17-year-old male patient with chronic diarrhoea and weight loss for several months presented. No other signs or symptoms. Scoliosis as personal medical history. A scheduled abdominal ultrasound was performed.

The ultrasound demonstrates multiple and well-delimited hypoechoic nodules with a hyperechogenic centre surrounding the hepatic hilum, which occupy the whole retroperitoneum and the presacral space (Fig 1, 2, 3, 4, 5). They do not show vascular flow in colour Doppler mode (Fig 6).

Before finishing the study, the radiologist evaluates soft tissue lesions in the skin of the patient and observes nodules with the same characteristics of the abdominal nodules (Fig 7). No other pathologic findings are seen.

A MRI is performed and it shows countless invasive and no-infiltrating nodular lesions that affect the subcutaneous tissue, all the dorsal, lumbar and sacral nerve roots, and the intra-abdominal nervous plexus (Fig 8, 9, 10, 11, 12). The findings are consistent with multiple superficial and deep neurofibromas because of neurofibromatosis type 1 (NF1).

Neurofibromas are benign tumours of nerve sheath cells of peripheral nerves. They may appear in a solitary or sporadic form, or they can be associated to neurofibromatosis type 1 (NF1). There are three types of neurofibromas: localised, diffuses and plexiforms, and NF1 may comprise an extensive affectation of these three lesions in different locations [1, 2, 3, 4].

Localised neurofibromas are lesions of superficial cutaneous nerves. In most cases, they are fusiform solitary slow-growing lesions that may be associated with mass effect (palpable lump) and painless [1, 3].

Diffuse neurofibromas are localised in the subcutaneous tissue and they are poorly defined lesions that can be observed as a plaque-like elevation of skin, predominantly in the head and neck [1, 3].

Plexiform neurofibromas affect a nerve plexus or a multiple fascicles in a medium-to large-sized nerve. The nerve enlargement is fusiform and tortuous, and it results in a pathognomonic appearance called “bag of worms”. They are considered a pathognomonic condition of NF1, and plexiform neurofibromas of the paraspinal and presacral region are the most common intra-abdominal neoplasm in NF1 [1, 3, 4]. Clinical presentation may comprise a subcutaneous mass, pain along the distribution of a nerve, effects related to local mass, and some patients may be asymptomatic [1, 2].
Ultrasound reveals a solid hypoechoic fusiform mass that may present a hyperechogenic centre with a hypoechoic central area that corresponds with the “target sign” in the MRI. These lesions may show vascular flow in Doppler mode [1, 4].
CT demonstrates a well-defined hypodense mass with minimal contrast enhancement or lack of enhancement [1, 2].
MRI shows a homogeneous mass isointense to muscle on T1-weighted images (T1WI) that is slightly hyperintense on T2-weighted images (T2WI) compared with surrounding fat. In some neurofibromas (70%) we may observe the “target sign”, which is a low signal intensity center on T2WI. On T1WI with contrast, neurofibromas have a heterogeneous enhancement [1, 2, 3].