8-year-old neutered male Boston Terrier

Recurrent pleural effusion of 6 months duration

Evaluated 6 months prior for labored breathing, was diagnosed with chylothorax and one month later had a thoracic duct ligation and pericardectomy, as well as a chest tube which was periodically drained until the effusion stopped. The patient had been doing well until 5 weeks prior to presentation, when shallow breathing recurred. When the chest was tapped, effusion was present which was no longer chylous but bloody and proteinaceous. Thoracocenthesis was repeated every few days until presentation, with amounts ranging between 300-900 ml each time.

On presentation the patient was mildly anemic (Hct 35.9%,  42-58.8%) with a stress leukogram (seg. neutrophils 92×10^3/ul, 2.7-8.5×10^3/ul; lymphocytes 0.424×10^3/ul, 0.5-1.4×10^3/ul).
Chem: mild hypoalbulinemia (3.1 g/dL, 3.3-4.2 g/dL)
Coags: WNL
TFAST: Moderate pleural effusion, no pericardial effusion, no masses seen.
Thoracic fluid analysis: PCV/TS: 9%/3.0 g/dL
– Cytology: exudate; large volume of red blood cells with mixed inflammatory population, erythrophagia.
– Triglycerides; 93 mg/dL, compared to 243 mg/dL in peripheral blood

AFAST: negative for free fluid


CT of the thorax and abdomen, precontrast and arterial phase.

CT of the thorax and abdomen, delayed phase.

Bone window, after contrast.

Computed tomography of the thorax and abdomen were acquired in 0.6 mm slices reconstructed in soft tissue and bone algorithms. Pre-contrast, arterial, and delayed post-contrast series were performed (Iohexol 350 mg/ml, 600 mg/kg IV via pressure injector).

In the caudal thorax, there are two non enhancing, spherical fluid-attenuating masses (pre-contrast HU: approximately 6.0 to 15.0), neither of which has a significant capsule. The largest (5.3 x 5.0 cm) is located in the caudal mediastinum, to the left of the oesophagus, extending from the tracheal bifurcation to the diaphragm. This mass causes severe rightward displacement of the esophagus and lateral displacement of the principal bronchi and and pulmonary vessels. There is concurrent compression and mild ventral displacement of the intrathoracic caudal vena cava; the accessory lung lobe is markedly reduced in volume and remains of  homogeneous in all phases.

The smaller mass (1.7 cm) is located dorsolateral to the oesophagus, ventral and to the right 6th and 7th thoracic vertebrae.

In the pleural space there is a moderate amount of fluid (14HU), which causes retraction and rounding of all lung lobes, with concurrent diffuse increase in attenuation (ground glass and/or consolidation).

A cranial mediastinal lymph node is mildly enlarged (1.4 cm) with irregular margins and heterogeneously enhancing. The right sternal lymph node (7.7mm) is heterogeneously enhancing with a nodular extension along the right internal thoracic vein, margins of which are ill-defined and thick.

In the right 8th rib, there is a segmental fracture and in the right 7th rib, there are multiple concave and circular radiolucencies, consistent with the previous surgical approach.

Axially in the cranial abdomen there is a large, lobular, fluid attenuating mass without a detectable capsule or enhancement. This mass measures approximately 5.4 cm. It is located ventrally to the first bifurcation of the coeliac artery and dorsally to the portal vein, causing marked ventral and rightward displacement of the latter. Its position corresponds to that of the right and left hepatic lymph nodes. There is a broad area of contact between the mass and the body of the pancreas, which is normal.

Dorsal to the left kidney, there is a similar fluid mass, its position corresponding to an aortic lymph node. The left adrenal gland is ventrally displaced by this fluid mass, and its caudal pole is moderately expanded 14.5mm) by fluid-attenuating, non-enhancing material, leaving a thin rim of tissue circumferentially.

In the left lateral lobe of the liver there is a fluid attenuating nodule  (2.4 cm) without enhancement or capsule. In the right liver, there are two smaller cystic nodules (<1.1 cm). In the gallbladder  is a mild amount of gravity-dependent mineral debris.

In the gastric fundus there are a 3 tubular mineral attenuating foreign bodies (3.5 cm x 0.9 cm). The remaining gastrointestinal tract, pancreas, spleen, right adrenal gland, urinary bladder and mesentery are normal.

Bilaterally the acetabula are shallow with poor coverage of the femoral heads and coxal joint incongruity, and moderate osteophytes are present.


1. Multiple unencapsulated fluid masses, abdomen, mediastinum and sub-pleural
Differential diagnoses include lymphangiomatosis vs. neoplasia (lymphangiosarcoma, hemangiosarcoma, mesothelioma).

2. Moderate pleural effusion and secondary pulmonary atelectasis
Differential diagnoses include chyle, hemorrhage or neoplastic effusion.

3. Cranial mediastinal lymphadenopathy (with cystic characteristics)

4. Cystic liver mass and nodules
Differentials include hepatic cysts, biliary neoplasia (cystadenoma, less likely cystadenocarcinoma) or metastatic disease from 1. Parasitic cysts appear unlikely with this presentation.

5. Cystic left adrenomegaly

6. Gastric foreign bodies, non-obstructive

7. Bilateral hip dysplasia and moderate coxarthrosis

A CT-lymphangiography via popliteal injection of contrast was performed (not shown here). Five scans were repeated over the abdomen over a period of 15 minutes showing a halt in the progression of iodine in a caudal aortic lymph node ipsilateral to the injection site.

An intercostal thoracotomy was performed. Intrathoracic cystic masses were drained, biopsied and omentalized, but could not be removed entirely.


Histology revealed densely cellular, unencapsulated, expansile and infiltrative masses comprised of a single population of neoplastic cells. The neoplastic cells were arranged into densely packed bundles and streams which multifocally formed variably sized, irregular vascular channels with multifocal intraluminal rafts, separated by eosinophilic acellular material. Cells were elongate to spindloid with indistinct cell borders, containing scant eosinophilic granular cytoplasm and a large, round to oval, finely stippled nucleus with two prominent nucleoli. Anisocytosis and anisokaryosis were marked with at least a five-fold variation in nuclear size. Mitotic figures were rare with five in 2.4 mm2 (equivalent to ten FN22/40X fields). Neutrophils were multifocally scattered among neoplastic cells. Hemorrhage and fibrin coalesced throughout the medullary sinuses. Draining macrophages were multifocally distended with hemosiderin pigment.

The presumptive histologic diagnosis at this point was hemangiosarcoma.

Immunohistochemistry for Factor VIII related antigen showed weakly to moderately immunoreactivity of the vascular clefts and strong immunoreactivity of the intravascular rafts.

Findings were consistent with malignant neoplasm of endothelium, and with the lesion distribution, lymphangiosarcoma was diagnosed.

The patient was lost to follow-up.


Lymphangiosarcoma is a rare malignant tumor that arises from lymphatic lining endothelium. In dogs, clinical signs usually involve severe lymphedema or subcutaneous masses1-4. In a large proportion of cases, dyspnea and exercise intolerance secondary to various degrees of pleural effusion are also seen as a reason for presentation1,4,5.  Mediastinal location6 and cystic abdominal masses7 have been described, as in the case presented here.

Hemangiosarcoma and lymphangiosarcoma can be challenging to differentiate microscopically with typical H&E staining. Immunohistochemical markers specific for lymphatic endothelial cells (Prospero-related homeobox gene 1 [PROX-1]) exist to confirm the diagnosis, which were unavailable at the time. Factor VIII related antigen, performed here, fails to differentiate between lymphangiosarcoma and HSA8.

In the case shown here, most cystic masses were associated with lymph centers, with the largest being consistent with the hepatic lymph nodes.

The location of the large cystic caudal mediastinal mass to the left of the esophagus excludes involvement of a diaphragmatic lymph node (shown in the Miller’s Anatomy of the Dog to the right of the esophagus) or involvement of the caudal mediastinal serous cavity9, also to the right of the esophagus. This cystic mass was presumed to be a metastasis within the lymphatics that run parallel to the esophagus.

The dorsal thoracic mass ventral to the right 6th and 7th ribs could correspond to that of an intercostal lymph node, said to be present in 25% of dogs ventrally to the rib heads at the 5th and 6th intercostal space10 This node drains to the cranial mediastinal centre, also abnormal in this case.

Lymphangiosarcoma is a rare but documented complication of chronic lymphedema, first reported in 1948 by Steward and Treves in chronically edematous extremities following radical mastectomy with lymph node resection. It is unknown whether the chronic chylothorax and thoracic duct ligation had any role to play in the development of this condition, as no imaging was performed prior to surgery.



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