Vascular leiomyoma, an uncommon soft tissue extremity lesion: Illustration of MR findings in 2 cases

Abstract

Vascular leiomyomas are infrequent benign soft tissue neoplasms arising from vascular wall. These lesions are more frequent in females, predominantly seen in lower extremities presenting as slowly enlarging freely mobile palpable soft tissue lesions, often painful. The role of imaging in small peripheral soft tissue masses is often limited to preoperative mapping with a long list of potential differentials. We are presenting 2 case studies of palpable masses with similar pathology, soft tissue vascular leiomyomas where its MR features can be helpful in inclusion of this entity not only in differential diagnosis of enhancing small peripheral soft tissue masses but can suggest a diagnosis in appropriate clinical scenario.

Background

Vascular leiomyomas also known as angioleiomyomas are a subcategory of leiomyomas originating from the tunica media layer of venous wall. The name itself indicates that it is a benign neoplasm commonly seen in dermis, subcutaneous adipose tissue or deep fascia. These are usually small tumors with female preponderance. Often presentation is with a painful mobile superficial palpable mass, more commonly in extremities with 50%-70% occurring in lower extremities [1]. When in males, they usually occur in upper extremities, head and neck region. By far their exact etiology is unknown.

MRI features of these lesions are seldom described in literature with mainly sporadic case reports. In this report we present two cases of histology proven vascular leiomyomas with emphasis on their MR findings and to include this as pertinent differential in peripheral enhancing soft tissue tumors.

Case presentation

Case 1

A 69-year-old woman presented with a palpable lump plantar aspect of her left foot, over fourth metatarsal. It started several years ago, was progressively increasing in size from last few months and associated with dull pain during weight bearing. No skin changes, redness or fever. No history of trauma or malignancy. During examination, a subcutaneous firm mass on the plantar aspect of fourth metatarsal was noted. The overlying skin was intact. No attachment to skin or deep tissues.

Ultrasound revealed a solid well defined lobulated hypoechoic mass measuring 1.8 × 1.5 × 0.8 cm (AP x TR x CC) in third intermetatarsal space with hypervascularity on Doppler interrogation. MRI without contrast revealed a solid well encapsulated subcutaneous mass plantar aspect of forefoot at level of fourth metatarsal head measuring 1.8 × 1.3 × 1 cm (AP x TR x CC), isointense to muscle on T1 weighted MR images (Fig. 1A). On T2 weighted images, a centrally heterogenous mass with peripheral hypointense rim was identified (Fig. 1B). Prominent subcutaneous vessel was identified in close proximity (lateral aspect) to the lesion (white arrowhead in Fig. 1B). No perilesional edema, mass effect or infiltration of surrounding structures was seen and the lesion was separate from plantar fascia. The MR findings were thought to be most in keeping with a mesenchymal or neurogenic tumor, most likely schwannoma from common plantar nerve.

Fig. 1.

A 69-year-old-female with soft tissue mass plantar aspect left fourth metatarsal. (A) Axial T1 weighted MR image demonstrating well circumscribed soft tissue mass isointense to skeletal muscle in plantar aspect of forefoot (black arrow). (B) The lesion is heterogeneously hyperintense on corresponding fat saturated axial T2 weighted MR image with peripheral hypointense rim representing fibrous capsule (curved arrow). As observed by Yoo et al (2009), subcutaneous vessel closely abutting lateral aspect of lesion (arrowhead).

Following surgical consultation, excision biopsy of the mass was performed. Histopathological examination revealed a well circumscribed neoplasm with fibrovascular connective tissue. The neoplastic cells were spindled and arranged in diffuse fascicles- some showing longitudinal fascicles and some oblique (Fig. 2A). The nuclei were elongated and show tapering or broad ends, with vesicular chromatin and occasional prominent nucleoli. Several blood vessels of varying caliber and wall thickness were present (Fig. 2, Fig. 2). No significant mitosis or necrosis. Immunohistochemistry demonstrated diffuse and intense immunoreactivity in the spindle cells of smooth muscle actin, muscle specific actin, desmin, and vimentin(Fig. 2C). Immunostains for CD 34, cytokeratin CAM 5.2 and S100 protein was negative. Based on above findings, histopathological diagnosis was compatible with vascular leiomyoma.

Fig. 2.

Pathology of soft tissue mass plantar aspect of left fourth metatarsal. (A) A well-circumscribed nodular lesion (left: black arrow) arising from the wall of an adjacent blood vessel (right: blue arrow). (B) Photomicroscopic image demonstrating lesion composed of sheets and fascicles of cytologically bland smooth muscle (purple arrows) throughout with increased numbers of blood vessels. The smooth muscle cells (purple arrows) often are arranged in a whirling pattern around blood vessels (H&E, X28). (C) Immunostaining for smooth muscle actin (X20) is strong and diffuse throughout the lesional cells(yellow arrows).

Case 2

A 29 year male presented with rapidly increasing painful soft tissue mass lateral aspect of his right knee for 4 months. On physical examination, there was a palpable mass without involvement of overlying skin or subcutaneous tissues. Patient was referred for an MRI which showed a focal, well defined lesion within anterolateral periarticular soft tissues of right knee appearing isointense to muscle on T1 and heterogeneously hyperintense on STIR images (Fig. 3A and B). No blooming on gradient recovery images (Fig. 3C). In post contrast imaging, there was uniform enhancement of the lesion (Fig. 3, Fig. 3). The lesion measured 2.3 × 1.4 × 1.9 cm (AP x TR x CC) and was insinuating through a smooth defect in iliotibial tract into subcutaneous soft tissues. No intra-articular extension or joint effusion. As noted in above case, there was a subcutaneous vessel abutting the anterolateral aspect of the lesion (orange arrow in Fig. 3, Fig. 3) The various differentials given based on MRI findings were slow flow venous malformation, solid mesenchymal tumor(benign/malignant). Patient was referred to Orthopedics. Biopsy followed by surgical excision was done with final diagnosis on histopathology compatible with vascular leiomyoma. As in Case 1, the lesion stains positive with smooth muscle actin and desmin.

Fig. 3.

A 29-year-old male with painful soft tissue mass right lateral knee. (A) Axial T1 weighted MR image shows well circumscribed soft tissue mass (white arrow) anterolateral aspect of right knee isointense to surrounding skeletal muscle. The lesion is insinuating through a defect in iliotibial tract (yellow arrow). (B) Axial fat saturated T2 weighted MR image shows intensely hyperintense mass with isointense areas within and peripheral hypointense rim (white arrows). Subcutaneous vessel in close proximity to anterior aspect of mass is noted (orange arrow). (C) Axial gradient recovery MR image showing no blooming. Orange arrow denotes small superficial vessel abutting the mass anteriorly. (D) axial pre and (E) post contrast T1 weighted fat saturated images demonstrating intense enhancement of the lesion.

Discussion

Vascular leiomyoma are benign soft tissue neoplasms comprising 5% of all benign soft tissue tumors [2]. They are more commonly seen in females involving lower extremities with the lesion presenting as palpable slowly enlarging soft tissue nodule. These can be seen over a wide age range, from third to seventh decade with most cases in third to fourth decade [3]. In males, they usually involve upper extremities, head and neck regions. Patient usually presents with pain, described as most common clinical feature in literature [4,5] and is thought to be due to localized ischemia secondary to smooth muscle contraction. Pain has been reported as the most striking clinical feature in series by Hachisuga et al. [5] and in 62% patients from a study at the Mayo Clinic [4]. Both of our patients presented in similar fashion with painful masses.

Regarding its pathogenesis, opinion is divided. Some authors believe that it's an intermediate stage from progression of hemangioma to simple leiomyoma due to smooth muscle proliferation [6]. Others believe these arise from tunica media of vessel wall. Various contributing etiological factors include minor trauma, venous stasis and infection; hormone fluctuation with estrogen [3].

Imaging wise, plain radiographs are the earliest and most cost effective for evaluation of soft tissue masses. In vascular leiomyomas, these are usually negative or with nonspecific soft tissue nodule distorting the subcutaneous planes. Dystrophic calcification or scalloping of the underlying bone can be rarely seen [7]. Sonography, most widely used for characterizing soft tissue lesions show nonspecific findings with the lesion appearing mostly hypoechoic. However, Park et al in their study in 2012 [8] suggested a common vascular pattern on doppler in these lesions comprising of cluster of several linear vessels converging to a single point. Sonography was performed in one of our cases with nonspecific findings of hypoechoic lesion with vascularity. Unfortunately, the images were not available. Regarding their size, Hachisuga et al in their study showed that 78% of these lesions were < 2 cms [5] whereas in our case knee lesion measured >2 cms in anteroposterior dimension.

On MRI, these lesions are usually isointense to the skeletal muscle on T1W images and iso to hyperintense to muscle on T2W with peripheral fibrous rim. Peripheral fibrous rim has iso to hypointense signal on T2 weighted images [9,10]. Correlation of MRI findings with histopathology has been well studied. According to Yoo et al [7], the lesion heterogenicity on T2W imaging is attributed to the abundance of tortuous vascular channels surrounded by smooth muscles and myxoid change. In their study, in post contrast images, mostly the lesions demonstrated intense homogenous enhancement while some showed peripheral enhancement. They also observed a vascular structure closely abutting the lesion in 7 out of their 8 patients. Occasionally, serpentine or curvilinear low signal intensity structures due to tortuous vascular channels on T1/T2W images can also be observed within the lesion [3,7].

Vascular leiomyoma was not included as the differential diagnosis in both of our cases with the final diagnosis made on histopathology following surgical excision. However, retrospectively reviewing the MR imaging revealed some striking MR features as observed by others, evident in form of T2 bright signal with variable heterogenicity, peripheral hypointense rim on T2 weighted images, intense post contrast enhancement (in one of our patients with knee lesion) and small abutting/closely adherent vessel at lesion periphery, also seen on histopathology, hence warranting more awareness for this relatively not so common entity. Location wise, lower limb involvement is uncommon in males, seen in one of our patients who was young male with lateral knee soft tissue mass.

The list of differentials for enhancing soft tissue mass on MRI is exhaustive ranging from benign neoplasms like neurogenic tumors, fibromas, glomus tumors, hemangiomas, angiolipomas, ganglion cysts etc. to malignant entities like sarcomas and malignant fibrous histiocytoma. The benign identities tend to be well defined whereas malignant lesions are ill defined and heterogenous. Often vascular leiomyomas form an important imaging differential to giant cell tumor, neurogenic tumor, and hemangioma [7,10]. In both of our cases, neurogenic tumor and hemangioma were the top differentials and vascular leiomyoma was not considered.

Histopathological examination in these tumors, as the name implies show smooth muscles and vascular channels without atypia with diagnosis often supported by immunohistochemical staining for vimentin, desmin, and smooth muscle actin which were positive in both of our cases [3,11]. Treatment is complete marginal excision with very rare recurrence rates after surgery [5].

Conclusion

In conclusion, our effort of presenting these 2 cases is not to suggest vascular leiomyoma as a sole diagnosis but to rather include it in the list of MR differentials for a painful slow growing subcutaneous extremity mass with T2 hyperintense signal and intense enhancement on post gadolinium imaging. Most other common identities are invariably mentioned by the radiologists in MRI reports with seldom inclusion of this lesser-known identity. Additionally, scrutiny for subtle MR features like intense enhancement, identifying closely abutting vascular structure at lesion periphery and hypointense peripheral rim on T2 weighted MR images can be a clue to suggesting this diagnosis and should be meticulously looked for.

Patient consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.