Soft tissue vascular malformations

Genetic syndromes and MRI diagnostics of vascular anomalies

Vascular malformations are frequently not standalone diseases, but part of more complex genetic disorders. The main syndromes associated with these anomalies include Klippel-Trénaunay syndrome (Klippel-Trénaunay syndrome), Sturge-Weber syndrome (Sturge-Weber syndrome), Maffucci syndrome (Maffucci syndrome), Proteus syndrome (Proteus syndrome), and blue rubber bleb naevus syndrome (Blue rubber bleb naevus syndrome).

Radiological imaging, particularly MRI, allows for a detailed study of the lesion structure. Typical MRI semiotics of a venous malformation (e.g., when localized in the foot) include the following features:

• On coronal T1-weighted images (T1WI), the lesion demonstrates a pronounced lobular structure, a hyperintense signal, and contains characteristic curvilinear areas of adipose tissue.
• On short-T1 inversion recovery (short-T1 inversion recovery, STIR) axial tomograms, the typical lobular morphology is also well visualized against a high (hyperintense) signal background.

Differential diagnosis: soft-tissue chondroma

When detecting soft-tissue mass lesions, it is necessary to perform a differential diagnosis with cartilaginous tumors, such as soft-tissue chondroma (soft-tissue chondroma). This is a lobular cartilaginous lesion composed of hyaline cartilage. On MRI, it demonstrates myxoid signal characteristics with heterogeneous low-signal areas caused by calcification processes.

On conventional radiographs, such a lesion appears as a soft-tissue mass with signs of punctate mineralization (punctate mineralisation). When evaluating T1WIs, subtle erosion of the adjacent bone structure, such as the articular head, can sometimes be detected.

The radiological differential series must include:

1. Periosteal chondroma (located deeply beneath the periosteum).
2. Synovial chondromatosis (affects tendon sheaths or originates from a joint).
3. Traumatic lesions (myositis ossificans, bizarre parosteal osteochondromatous proliferation — BPOP).
4. Gouty tophi and calcification in connective tissue disorders.

A separate entity is paraarticular chondroma, which results from cartilaginous metaplasia of the joint capsule. Most commonly localized in Hoffa's fat pad and may eventually progress to ossification, transforming into an extraskeletal osteochondroma.

Peripheral nerve mass lesions

Peripheral nerve tumors are another common cause of soft tissue masses. They are divided into true neurogenic tumors and pseudotumors. Benign true nerve sheath tumors include:

Schwannoma (neurilemoma, NL) — a slow-growing tumor originating from Schwann cells. Usually solitary, but multiple lesions occur in neurofibromatosis type 2 (NF2) or schwannomatosis.

Neurofibroma (NF) — accounts for about 5% of all benign soft tissue neoplasms. There are three types (all can occur in neurofibromatosis type 1 — NF1):

• Localized: the most common type (>90%). Grows from small branches or major nerves. Usually solitary, not associated with NF1 (but can be multiple in NF1).
• Diffuse: appears as diffuse thickening of the skin and subcutaneous tissue. Associated with NF1 in 10% of cases.
• Plexiform: a pathognomonic sign of NF1. Infiltrates a major nerve, spreading to adjacent tissues. Has a lobular structure resembling a "bag of worms" (bag of worms).

Radiological features of nerve sheath tumors

To determine the benign nature of a nerve tumor, a number of specific imaging signs are used:

• Fusiform shape along the long axis of the nerve and anatomical continuity with it.
• Split nerve sign (target/entering-exiting nerve sign): in neurilemomas, the nerve is often located eccentrically, whereas in neurofibromas, it runs strictly centrally.
• Split-fat sign (split-fat sign): the growing tumor expands the surrounding fat rim of the intermuscular space.
• Fascicular sign: ring-like areas of hypointense signal within the lesion on PD or T2WI, corresponding to nerve fiber bundles.
• Target sign (target sign): on T2WI, a low signal is determined in the center (fibrous tissue), and a hyperintense signal (myxoid content) is observed at the periphery.

It is important to remember: despite the abundance of signs, it is impossible to reliably distinguish a schwannoma from a neurofibroma solely using ultrasound or MRI. Furthermore, degenerative changes in neurilemomas can lead to cavitation, hemorrhage, and calcification, masking the true neurogenic nature of the lesion. One should also maintain vigilance regarding malignant peripheral nerve sheath tumors (MPNST), the risk of which reaches 8–12% in NF1.

Class and exam questions

What else to study on this topic

• Malignant peripheral nerve sheath tumors (MPNST)
• Bizarre parosteal osteochondromatous proliferation (BPOP)
• Maffucci syndrome and vascular anomalies
• Neurofibromatosis type 1 (NF1) and plexiform neurofibromas

Other topics in the "Musculoskeletal System" section

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