Vascular anomalies are a heterogeneous group of pathologies of the circulatory system characterized by morpho-structural and/or functional alterations of various nature, severity and extent that can affect any type of blood and/or lymphatic vessel, of any caliber and anatomical district.
The new ISSVA (International Society for the Study of Vascular Anomalies) classification, approved at the 20th Workshop in Melbourne-April 2014 and revised in May 2018, is the most standardized and accepted classification; it distinguishes two different categories: vascular tumors and vascular malformations.
Vascular malformations are divided into simple, combined or associated with other anomalies.
Based on their hemodynamic characteristics they are further distinguished in low flow forms (capillary, lymphatic, venous) when there is no arterial component and high flow forms (arteriovenous and arteriovenous fistulas) when arterial component is present.
Capillary malformations (CM) are low-flow vascular anomalies that are localized in the skin and mucous membranes and present as congenital spots ranging in color from pink to red-purple.
They are potentially ubiquitous, but most of them are found in the neck region.
The diagnosis of capillary malformation is clinical.
Venous malformations (VM) are congenital anomalies of the central or peripheral venous system and they are more frequently localized in soft tissues and skin.
They are usually observed in the head and neck, trunk and extremities.
The most frequent localizations are superficial, cutaneous and mucous localizations but deep, intramuscular, intraosseous or visceral localizations are also observed.
Clinically, they present as bluish lesions that expand with Valsalva manoeuvre and following compression.
The new reviewed ISSVA classification includes the glomuvenous malformation as a subtype of venous malformation.
Venous malformations are usually septated lesions with low or intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted and T2 fat suppressed images.
Detection of phleboliths is helpful for diagnosis of venous malformations; they appear as small low signal intensity foci.
Arteriovenous malformations or AVMs are defined as anomalous communications between arterial and venous vessels, connected to each other directly or through a network of vessels called “nidus”.
Clinical manifestation of AVMs are purple or reddish colouration of the skin, local hyperthermia, dilated skin vessels; other typical signs are pulsating sensation and thrill.
In the most severe cases of disease, pain, bleeding and ulcers may appear.
Arteriovenous malformations are typically congenital and increase in size with the growth of the child.
AVMs may be single, multiple or part of a genetic disorder.
MR imaging findings include enlarged feeding arteries and draining veins, in the absence of a well-defined mass. Early venous filling is typically seen on dynamic contrast-enhanced sequences.
Lymphatic malformations (LM) are the second most common type of vascular malformation after venous malformations. Clinically, they appear as not compressible, not painful, smooth soft-tissue masses, usually in the neck and axillary regions.
Lymphatic malformations are commonly associated with venous malformations, configuring combined lymphatic-venous malformations.
They can gradually increase in volume over the years.
Lymphatic malformations can be divided into macrocystic, microcystic and mixed cystic types.
MR imaging findings are lobulated, septated masses with low or intermediate signal intensity on T1-weighted images, high signal intensity on T2-weighted and T2 fat suppressed images. In some cases internal fluid-fluid levels can be observed.
After i.v. gadolinium injection microcystic lymphatic malformations do not show enhancement, whereas macrocystic lymphatic malformations can show rim and septal enhancement.
The MRI protocol used at our Hospital for clinical suspicion of vascular malformation is performed with 1,5 T scanner and phased-array coils.
MRI SEQUENCES
- Localizer sequence
- Coronal steady-state free precession sequence (section thickness 3 mm) helps to localize and to define the spatial extension of the malformation
- Axial, coronal or sagittal T2-weighted FSE sequences (section thickness 4 mm) are used to tissue characterization, to evaluate degree of signal hyperintensity and to look for flow-voids, phleboliths and fluid-hemorrhage levels
- Axial T1-weighted FSE sequence (section thickness 4 mm) is used to define the anatomical relationships of the lesions with the surrounding tissues
- Axial or coronal fat suppressed T2-weighted FSE sequence (section thickness 4 mm)
- Axial DWI SE EPI (section thickness 5 mm; b-value 0, 500, 1200 s/mm2)
- 4D Time Resolved MR Angiography with reconstruction or dynamic axial T1-weighted 3D gradient-echo fat-suppressed sequences (section thickness 2 mm) after i.v. injection of paramagnetic contrast agent are used to evaluate vascular anatomy (feeding and draining vessels) and are essential for surgical planning; we use an injection rate of 1.5 cc/s of 0.1 mmol/kg gadolinium-based contrast, followed by a 10 cc saline flush at the same rate
- Axial contrast-enhanced T1-weighted 3D gradient-echo fat-suppressed sequence (section thickness 1 mm) with multiplanar reconstructions is used to evaluate delayed enhancement
PROPOSAL OF A SIMPLE FLOW CHART TO GUIDE DIAGNOSIS WITH MRI
*Flow voids are areas of no signal due to blood flowing out of the section before the signal can be sampled; they are due to rapid flow in arteries and to turbulence-related dephasing. Flow voids appear as tubular structures without signal intensity on pulse sequences and they correlate with the presence of pathological vessels.
CASE 1
10-yo boy with pain and slight swelling on right deltoid area, without alteration in skin pigmentation.
CASE 2
12-yo boy with warm swelling of right arm, pain and thrombophlebitis.
CASE 3
3-yo child with a soft, compressible, mass in the right arm.
CASE 4
16-yo girl with swelling of left leg, pain and edema of the subcutaneous adipose tissue.
CASE 5
15-yo girl with a small, painful, compressible blue swelling located in the skin and subcutaneous tissue of the right foot.
CASE 6
14-yo girl with warm palpable swelling in right axillary area characterized by trill and purple skin discoloration.
CASE 7
6-months-old child with large soft tissue mass within the left chest with palpable bruit and blue-purple skin discoloration.
CASE 8
8-yo boy with a left scapular mass with pain, fever, cutaneous inflammation and thrombophlebitis.
CASE 9
11-yo girl with posterior cervical painless compressible mass with blue skin discoloration.
CASE 10
12-yo girl with painful compressible soft tissue mass of left distal thigh, with blue skin discoloration.
