History
A 10-year-old female donkey was evaluated because of a large soft tissue mass over the right tarsus. The patient had no history of trauma and began to develop the mass 12 months prior to evaluation. On palpation, the mass was compressible and movable. Subcutaneous fluid was detected, and there were no signs of pain on palpation of the lesion. The donkey was sound during serial lameness examinations, and results of hematologic and serum biochemical analyses were unremarkable. Radiographs of the right tarsus were obtained (Figure 1).
Lateral (A) and dorsoplantar (B) radiographic images of the right tarsus of a 10-year-old female donkey evaluated because of swelling over the tarsal area of 1 year's duration.
Citation: Journal of the American Veterinary Medical Association 242, 5; 10.2460/javma.242.5.611
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Centered at the right tarsus, there is severe extracapsular soft tissue swelling that extends proximally over the distal aspect of the tibia and distally over the proximal aspect of the metatarsal region. At the caudodistal aspect of the right tibia, a focal area of smoothly marginated new bone is evident at the level of the closed distal tibial physis. No additional osseous abnormalities or degenerative joint disease of the tarsus are present.
The proliferative new bone formation was considered clinically unimportant and most likely a periosteal reaction secondary to the soft tissue mass or physiologic bone remodeling at the closed distal tibial physis. Because of the lack of radiographic evidence of bone lysis, an aggressive bone lesion was ruled out.
To better access the soft tissue structures, grayscale ultrasonographic examination of the right tarsus was performed with a sector array transducer at 6.6 and 8.0 MHz (Figure 2). Ultrasonographically, the subcutaneous tissues were thickened (3 to 6 cm) and diffusely contained a matrix of innumerable tubular structures (diameter, < 5 mm) that were distended with anechoic fluid. Color-flow and power Doppler ultrasonography were used to evaluate the small tubular structures; a Doppler shift was not detected. The tubular septa (diameter, 3 to 10 mm) were hyperechoic, and within individual septa, vascular structures were detected with power Doppler interrogation. In the far field, the joint capsule of the right tibiotarsal joint was intact, indicating that the soft tissue swelling and fluid-filled structures were extracapsular. Additionally, right hind limb extensor tendons and the right saphenous vein were observed adjacent to the osseous margins of the tarsus and not involved with the subcutaneous lesion. Differential diagnoses for an extracapsular subcutaneous mass containing nonvascular fluid-filled channels included cutaneous neoplasia or cutaneous hamartoma.
Ultrasonographic images of the subcutaneous tissues of the right tarsus of the same donkey as in Figure 1; images were acquired with a sector array transducer. A—Transverse ultrasonographic image (6.6 MHz; depth, 7 cm) of subcutaneous tissue at the dorsal aspect of the proximal intertarsal joint. Within the subcutaneous tissues, multiple hyperechoic septa (arrowheads) separating anechoic cavitations (arrow) with distal acoustic enhancement are evident. B—Longitudinal ultrasonographic image (6.6 MHz; depth, 12 cm) of subcutaneous tissue at the dorsal aspect of the distal portion of the tibia, tarsus, and third metatarsal bone. Notice the extracapsular subcutaneous extent of the tumor (arrowheads). C—Transverse ultrasonographic image (8.0 MHz; depth, 12 cm) of subcutaneous tissue at the lateral aspect of the talus with application of power Doppler ultrasonography to identify vasculature within the lymphangioma septa. Notice that a Doppler shift was not detected (arrows).
Citation: Journal of the American Veterinary Medical Association 242, 5; 10.2460/javma.242.5.611
Treatment and Outcome
The donkey was premedicated with detomidine (20 μg/kg [9.1 μg/lb], IV) and anesthetized with propofol (2 mg/kg [0.9 mg/lb], IV). Biopsy specimens of the mass were obtained for histologic examination. Fluid samples from the mass were obtained and submitted for bacterial culture; no growth was observed after 72 hours in culture.
On histologic examination of H&E-stained sections of the mass, the dermis and the subcutis tissue of the affected right hind limb contained multiple, variably sized cavernous spaces lined by a single layer of attenuated, oval to elongated endothelial-like cells. On histologic examination of periodic acid-Schiff-stained sections, a basement membrane was not found beneath the endothelium lining the cavernous spaces. Neoplastic cells had a moderate amount of slightly basophilic homogeneous cytoplasm and an oval to elongated centrally located nucleus. Chromatin was predominantly hyperchromatic and, less commonly, vacuolated with a single prominent amphophilic nucleolus. Mitotic figures were rare. A histopathologic diagnosis of cutaneous lymphangioma was made.
Because of the location of the lymphangioma directly over the right tarsus, bulk surgical removal of the mass was not a treatment option. Additionally, given that the patient had no signs of pain on palpation and no lameness was observed, this mass was considered an incidental finding.
Comments
Cutaneous lymphangioma is a benign, locally invasive tumor of the lymphatic system. These lesions occur rarely in both human and veterinary patients. Lymphangiomas have been described as both neoplasms and hamartomas or congenital malformations of the lymphatic system. These tumors are reported to account for only 0.1% of all cutaneous neoplasms in horses1; to our knowledge, cutaneous lymphangioma has never been found in a donkey. Lymphangiomas form from the proliferation of lymphoid epithelium that coalesces into anomalous lymphatic vessels surrounded by fibrous tissue and vasculature. These tumors occur most often near the embryological sites of lymph sac development and are believed to stem from congenital lymphatic malformations.2 At the sites of tumor formation, lymphatic tissue proliferates without connecting and draining to the venous system. Because of the congenital association of these tumors, most lymphangiomas are found in young patients; however, adult-onset lymphangiomas also occur in humans.2 Adult-onset or acquired lymphangiomas occur rarely and are most often secondary to surgical trauma, infection, inflammation, or lymphatic obstructions.2 For the donkey of the present report, proliferative new bone was detected radiographically at the caudodistal aspect of the left tibia. Although this new bone may represent a periosteal reaction secondary to the lymphangioma, both the lack of bone lysis and mature age of the patient rule out congenital bone involvement.
The ultrasonographic characteristics of cutaneous lymphangioma have been described in a horse as unencapsulated fluid-containing tubules in a honeycomb pattern.3 Two-dimensional and 3-D ultrasonography are used to detect lymphangioma in the subcutaneous tissues of the fetus before parturition.4 As was done for the donkey of the present report, Doppler ultrasonography is used in humans with scrotal cystic lymphangioma to identify septal vasculature.5 Diagnosis of lymphangioma without histologic evaluation is facilitated by ultrasonography in human patients. Lymphangioma in horses has similar imaging characteristics to human lymphangioma, and therefore, diagnosis of lymphangioma with ultrasonography alone may be achievable in veterinary patients as well.
Ultrasonography and radiography together were invaluable when assessing the mass of the donkey of the present report, and although rare, the unique imaging characteristics of this lesion have been documented previously. Although the donkey of the present report was an adult, because of the congenital nature of these tumors, the mass was most likely present at birth, slowly grew over time, and was not noticed until the patient reached 9 years of age. Lymphangiomas continue to grow as a patient ages, so if left untreated, these lesions should be serially monitored to ensure they are not causing clinically relevant problems.
1. Scott DW, Miller WH. Neoplastic and non-neoplastic tumors. In: Scott DW, Miller WH, eds. Equine dermatology. St Louis: Elsevier Science, 2003; 745–746.
2. Wiegand S, Eivazi B, Barth PJ, et al. Pathogenesis of lymphangiomas. Virchows Arch 2008; 453: 1–8.
3. Gehlen H, Wohlsein P. Cutaneous lymphangioma in a young Standardbred mare. Equine Vet J 2000; 32: 86–88.
4. Paladini P, Vassallo M, Sglavo G, et al. Cavernous lymphangioma of the face and neck: prenatal diagnosis by three-dimensional ultrasound. Ultrasound Obstet Gynecol 2005; 26: 300–302.
5. Loberant N, Chernihovski A, Goldsfeld M, et al. Role of Doppler sonography in the diagnosis of cystic lymphangioma of the scrotum. J Clin Ultrasound 2002; 30: 384–387.
