Summary: An 82-year-old man with a history of hypertension presented for routine
ultrasound surveillance of a known abdominal aortic aneurysm.
Incidentally noted was a solid, hypoechoic mass interposed between the
spleen and superior aspect of the left kidney. The patient was referred
for surgical evaluation. On clinical examination, he was asymptomatic
without gross hematuria, left flank pain, weight loss, bony pain, or
abdominal distention. There was no family history of renal cell
carcinoma. The only medication he took was Atenolol. His surgical
history was limited to pilonidal cyst excision. The patient was a
retired corporate executive with a 20 pack-year history of smoking and
no known asbestos exposure. His vital signs were: afebrile, pulse 80
bpm, blood pressure 132/74 mmHg, and respiration 20. On physical exam
his abdomen was soft, with a palpable aneurysm. No fluid wave or
costovertebral angle tenderness was present. Urinalysis was negative for
blood and leukocytes.
Localized splenic malignant mesothelioma
Initial ultrasound examination demonstrated the patient’s known
infrarenal abdominal aortic aneurysm and discovered a 3 × 4 cm solid,
slightly lobulated, hypoechoic mass contiguous with the upper pole of
the left kidney and adjacent to the spleen. It did not contain any
calcifications (Figure 1). Concern for a renal or adrenal neoplasm
prompted further evaluation with computed tomography (CT).
CT of the abdomen and pelvis revealed a 4.3 × 3.9 cm enhancing solid
mass superior and anterior to the left kidney with a fat plane
separating the mass from the left adrenal and left kidney. The mass
surrounded the inferior tip of the spleen without distorting the
parenchyma, suggesting containment by the splenic capsule (Figure 2).
magnetic resonance imaging (MRI) was performed to further characterize
the mass. MRI showed an ovoid T1 and T2 intermediate, heterogeneously
enhancing exophytic splenic lesion (Figures 3 and 4). The left kidney,
left adrenal gland, pancreatic tail, liver, and gall bladder were
normal. There was no lymphadenopathy.
Chest x-ray demonstrated hyperinflation without pleural plaque, effusion, mass, or infiltrate.
resection with splenectomy and distal pancreatectomy was performed.
Pathology revealed a tumor arising from the splenic capsule, or possibly
from a mesothelial inclusion within a splenic hilar node (Figure 5).
The tumor was surrounded by lymphoid appearing cells and portions of a
fibrous-like capsule. The splenic parenchyma was uninvolved (Figure
6).There was no splenomegaly. Additional splenic hilar nodes were
negative for tumor. The tumor cells stained positive for mesothelial
markers calretinin, keratin 5/6, keratin AE1/3, and CAM 5.2.
Adenocarcinoma and melanoma markers were negative. The
immunohistochemical features were consistent with mesothelioma.
Malignant mesothelioma is a neoplasm arising from the mesothelial
cells of the serosal surfaces of the pleura and peritoneum. On rare
occasions, mesothelioma is found to arise from the pericardium or tunica
vaginalis.1 Nearly 85% of all mesotheliomas arise from the pleura, while approximately 9% arise in the peritoneum.2
Diffuse malignant mesotheliomas should be differentiated from localized
malignant mesothelioma, as the latter is incidental at presentation,
requires surgical treatment, and portends a
The risk of mesothelioma in the United States is approximately 11/1,000,000 Americans per year.4
Median survival is generally 12 months. Peak incidence is in the fifth
and sixth decades. The tumor characteristically has a poor response to
multimodality therapy. The worldwide incidence of malignant mesothelioma
is on the rise and is not expected to peak for another 10 to 20 years.5
initial cases demonstrating a causal relationship between occupational
exposure to asbestos and development of malignant mesothelioma were
described at the blue-asbestos mine in Wittenboom, Australia, in the
1960’s.6 A latency period of 20 to 30 years from exposure to disease presentation is common.7
Mesothelioma is also reported to have occurred in thoracotomy wounds,
previous drainage sites, and ports of prior radiation. A possible
association with simian virus 40 is also being explored.5
clinical features of peritoneal mesothelioma include abdominal pain,
mass, distension, ascites, and thrombocytosis. In contrast to diffuse
malignant mesothelioma, localized malignant mesothelioma is most often
an incidental finding. Localized malignant mesothelioma presents as a
well circumscribed tumor of the serosal membranes with the microsopic
appearance of diffuse malignant mesothelioma. There is no evidence of
organ encasement or studding by tumor.
Little has been reported
about localized malignant mesothelioma. In a series of 23 patients with
localized malignant mesothelioma described by Allen TC, et al., 21 (91%)
were pleural based, while 2 (9%) were peritoneal.3 The age at mean presentation was 63 years with a male:female ratio of 2:1.
tomography and/or MRI of localized splenic malignant mesothelioma has
not been reported to our knowledge. This case demonstrates the expected
characteristics of a soft tissue tumor; sharply demarcated,
heterogeneously enhancing without dystrophic calcifications. No
metastatic lesions were found upon initial imaging or at one-year follow
up. Adjuvant chemotherapy and radiation therapy were not undertaken.
diagnosis of a mass localized to the splenic hilum includes primary and
secondary neoplasm as well as infectious etiologies. Respectively,
these are angiosarcoma, GI stromal tumor, lymphoma, metastatic
adenocarcinoma, and granulomatous disease such as tuberculosis. Imaging
findings are not sufficiently distinctive to allow a specific diagnosis.
Diagnosis may come at surgery or be possible via percutaneous biopsy if
the anatomy is favorable.
Localized malignant mesothelioma is
histologically, immunohistochemically, and ultrastructurally identical
to diffuse malignant mesothelioma. Epithelial-types predominate with the
remainder being sarcomatous or mixed. Light microscopy of malignant
epithelioid mesothelioma is characterized by sheets of polygonal cells
with abundant eosinophilic cytoplasm, round nuclei, and prominent
nucleoli.2 All mesotheliomas stain positive for keratin. The
best immunohistochemical markers for differentiating epithelial
malignant mesotheliomas from papillary serous carcinomas are calretinin,
thrombomodulin and keratin 5/6 positivity.2 Calretinin has
the highest sensitivity for malignant epitheliod mesothelioma.
Negativity for adenocarcinoma markers such as CEA and TTF-1 are
The prognosis for localized malignant
mesothelioma is favorable compared to diffuse malignant mesothelioma.
Cytoreductive surgery and intraperitoneal chemotherapy are treatment
options for diffuse malignant mesothelioma, whereas most cases of
localized malignant mesothelioma are cured by surgical excision.
This case illustrates the presentation of a rare entity, localized
splenic malignant mesothelioma. Recognition and differentiation of
localized mesothelioma from diffuse malignant mesothelioma is critical,
as their treatment options and prognosis are vastly different. Localized
malignant mesothelioma is most often an incidental finding at
presentation and cured by surgical excision.
- Winstanley AM, Landon G, Berney D, et al. Immunohistochemical
profile of malignant mesotheliomas of the tunica vaginalis: A study of
20 cases. Am J Surg Pathol. 2006;30:1-6.
- Busch JM, Kruskal JB, Wu B. Best cases from the AFIP malignant meosthelioma. Radiographics. 2002;22:1511-1515.
- Allen TC, Cagle PT, Churg AM, et al. Localized malignant mesothelioma. Am J Surg Pathol. 2005:866-873.
- Antman K, Hassan R, Eisner M, et al. Update of malignant mesothelioma. Oncology (Williston Park). 2005;19:1301-9; discussion 1309-1310, 1313-1316.
- Robinson BWS, Lake RA. Medical progress: Advances in malignant mesothelioma. NEJM. 2005;353;1591-1603.
- Leigh J, Robinson BWS. The history of mesothelioma in Australia 1945-2001. In: Robinson BWS, Chahinian PA, eds. Mesothelioma. London: Martin Dunitz, 2002:55-110.
T, Haveric N, Carmignan CP,et al. Abdominal computed tomography scans
in the selection of patients with malignant mesothelioma for
comprehensive treatment with cytoreductive surgery and perioperative
intraperitoneal chemotherapy. Cancer. 2005;103:839-849.