Differential diagnosis of intramuscular venous malformation

33-year-old patient who feels healthy. However, he has had recurrent pain and left lumbar swelling for almost 2 years. In an MRI to exclude a herniated disc, an unclear tumor is found. Presentation for biopsy and further clarification of the lesion. Infrared thermography (right) shows no local warmth or change in perfusion in the area of the pain. Currently no swelling or skin discoloration in the photograph (left).

The lesion is very clearly visible in the MRI in coronal plane. In the T2-weighted sequence with fat saturation (left), the lesion is highly hyperintense (white). In the non-enhanced T1-weighted sequence (right), it is virtually isointense to the surrounding back muscle. Note here the fatty tissue visible marginally in the lesion, hyperintense in T1 weighting.

In the axial T2-weighted MRI sequence, the lesion is located in the erector spinae back muscles. Classic fluid-fluid level due to gravity-induced sedimentation effects with the patient lying still in the supine position in the MRI unit.

In dynamic contrast-enhanced MR angiography (late phase over 2 min after contrast administration, left coronal and right sagittal), the lesion shows no contrast enhancement or increased vascularization. It is practically invisible.

In the axial, fat-saturated T1-weighted images after contrast medium administration, an initially inhomogeneous accumulation of contrast medium in terms of contrast pooling occurs only slowly and incompletely. This is also relatively typical of a venous malformation.

An ultrasound-guided punch biopsy with a thin 16-gauge biopsy needle is performed immediately afterwards. Only minor bleeding occurs during needle biopsy, which is quickly stopped by compression. Note the dark red tissue fragment obtained, which macroscopically looks almost like a thrombus but consists of the blood-filled dysplastic cavities of the venous malformation.

Histopathological section; hematoxylin & eosin (HE) stain, 90x magnification of the punch cylinder. Punch cylinder showing parts of venous malformation with densely packed, irregularly configured large-caliber venous vessel parts. These do not appear tubular as in a normal mature vessel, but as if the vessels are "everted". The lumen looks solid and blood is all around the outside.

Histopathological section; hematoxylin & eosin stain (HE), 160x magnification of the punch cylinder. Here it is clear to see that the irregular, blood-filled spaces of the venous malformation are not solid, but are "voids" partially filled with erythrocytes. The endothelial lining corresponds to the outer border of the visible lesion.

Histopathological section; CD31 stain for specific staining of vascular endothelial cells, which then stain dark brown. 80x magnification of the punch cylinder. This proves that the outer cellular boundary of the visible lesion corresponds to blood vessel endothelia.

Histopathological section; Elastica van Gieson (EvG) staining of collagen and connective tissue. 90x magnification of the punch cylinder. EvG connective tissue staining illustrates the dysplastic wall structure of the malformation with yellow-stained smooth muscle fiber tracts intermixed with red-stained connective tissue areas and interspersed delicate black elastic fibers. This structure is actually typical of venous vessels, but the irregular structure depicted here is atypical and indicates the malformed venous wall structure of the venous malformation.

Histopathological section; the immunohistological staining against smooth muscle actin (SMA) demonstrates the irregular, dysplastic wall structure of the vessels of the venous malformation particularly well. A normal, ordered smooth muscle wall structure is not present. The lesion is asymmetrically interspersed with irregular SMA-positive smooth muscle.

Histopathological section; immunohistological staining using MIB-1 for the Ki67 antigen is a classic stain to show the proliferation activity of a lesion. As a proliferation marker, Ki67 indicates all cells undergoing cell division in the broadest sense (outside the G0 phase in the cell cycle). Here, only very few actively dividing nuclei (here without mitotic spindles) are detectable as positive nuclear staining. Thus, a very low proliferation rate is an indication of a benign lesion.