Primary splenic hemangiopericytoma
The sonographic images demonstrate a complex lesion measuring 5.6
cm in greatest dimension within the superior portion of the spleen
adjacent to the left hemidiaphragm. CT imaging shows the mass to
have an enhancing rim with areas of lower density internally. The
mass lies above the splenic hilum, and is posterior and lateral to
the stomach, causing compression along the greater curvature. No
other significant intra-abdominal pathology was identified.
At the time of surgery, the splenic mass was noted to be
adherent to the stomach and diaphragm. Additionally, multiple dense
adhesions of the omentum were observed in the left upper quadrant.
The adhesions were lysed and a splenectomy performed. Pathologic
examination revealed a spleen weighing 240 grams and measuring 13 x
11 x 5 cm. A multinodular mass at an area of surface disruption of
the spleen was found and measured 4.5 x 4.0 x 2.0 cm. Microscopic
evaluation revealed diffuse proliferation of spindle cells. The
tumor cells showed mild to moderate nuclear atypia and high mitotic
activity. Large areas of necrosis and hemorrhage were also
identified. One lymph node was recovered and showed no evidence of
neoplasm. The tumor cells were positive for vimentin and negative
for keratin, S-100 protein, HMB-45, actin, and desmin. Additional
immunostains also revealed that the tumor cells were positive for
CD34. Given this constellation of findings, a diagnosis of
hemangiopericytoma was made.
This case provides many interesting points of discussion.
Initially, the choice was made to proceed with fine-needle
aspiration to provide a diagnosis. Percutaneous needle biopsy of
the spleen has been shown to be a safe method for obtaining tissue
samples. In the past, clinicians were reluctant to perform this
procedure due to the splenic vascularity and difficulty in safe
access because of the adjacent colon and lung pleura. Quinn et
reported a series of 35 percutaneous interventions
of the spleen including percutaneous biopsy, therapeutic and
diagnostic fluid aspiration, and catheter drainage of abscesses in
which they encountered no complications. Biopsies in their series
were performed using 22g or 20g needles. In our case, a 20g needle
was used and three passes were made under CT guidance. No
complications were encountered. The potential benefit of needle
aspiration biopsy is spleen preservation in certain instances. In
this case, the aspirate consisted of necrotic material, and tumor
could not be ruled out. Because of these considerations, the
decision was made to proceed with splenectomy.
Due the rarity of focal splenic lesions, it may be useful to
review the differential diagnosis of this important entity. The
differential diagnosis is wide and includes posttraumatic,
infectious, vascular, and neoplastic categories.
Different imaging methods are available to assess focal splenic
lesions, although there is not one clearly superior imaging
modality. Scintigraphy will show intrasplenic masses as areas of
decreased uptake, but no distinction is possible between solid and
cystic structures. CT can image lesions accurately and reveal their
relationship to surrounding organs. However, splenic masses with
Hounsfield unit measurements similar to that of normal splenic
parenchyma may be missed. Additionally, the sinusoidal circulation
of blood through the spleen causes heterogeneity to its appearance
with IV contrast administration. Sonography allows differentiation
of solid from cystic masses, but no sonographic criteria yet exist
to reliably distinguish benign from malignant solid lesions. Also,
cyst-like lesions can result from multiple different causes that
often cannot be differentiated with ultrasonography.
Splenic cysts belong in a distinct subcategory with a more
limited differential diagnosis. Splenic cysts are relatively rare
compared with solid lesions. They may be classified as true cysts,
in which the cyst is lined with specific secreting membrane or has
a parasitic lining. On a worldwide basis, hydatid cysts from
echinococcal infection are thought to represent two thirds of all
splenic cysts.2 In North America, however, this entity
is exceedingly rare. Patients are not usually febrile unless
secondary infection of the cyst has developed. Treatment of these
hydatid cysts is by surgical removal. The other type of true cyst
is a congenital epithelial cyst. Histologically, these cysts have
an epithelial lining and one theory is that they originate from
peritoneal mesothelial cells that have become trapped within the
splenic parenchyma during development. Another general type of
splenic cyst is the pseudocyst, which is the most common type of
splenic cyst in the United States and occurs most commonly after
trauma. These pseudocysts are thought to represent the final stage
of evolution of splenic hematomas. Histologically, they are not
lined by epithelium. When encountering a primarily cystic splenic
mass, other causes to consider are abscess, cystic neoplasm, and
intrasplenic pancreatic pseudocyst.
In a significant number of patients with blunt abdominal trauma,
splenic rupture and hematoma formation occur. The echogenicity of
splenic hematomas varies depending on the stage of evolution. Soon
after trauma, these lesions tend to appear as hypoechoic
intra-parenchymal lesions. A "double contour" sign may indicate a
subcapsular component of the hematoma.3 When the
hematomas become chronic, they tend to become more cystic.
Another possibility in the differential diagnosis of focal
splenic lesions is infection. The main predisposing factor for
splenic infection is immunosuppression. Because of the increasing
number of immunocompromised patients secondary to AIDS,
posttransplant immunosuppression drugs, and cancer chemotherapy
treatments, splenic infections and abscess formation have become
more prevalent over the past few decades. Other predisposing
factors for infection include diabetes, sickle cell anemia, and
parenchymal disruption from trauma or infarction. Infections in the
spleen are most commonly caused by staphylococcus and
streptococcus, but fungal infections also constitute a good
percentage of cases. Although it is difficult to determine
bacterial versus fungal etiologies based on imaging characteristics
alone, one study has shown that unilocular abscesses have a
bacterial etiology in 94% of cases.4 This same study
also found that if the abscess is multilocular, a fungal etiology
is the cause 64% of the time. Splenic infection usually occurs by
hematogenous seeding from a primary source elsewhere in the body.
Another more rare route of infection is by direct spread from
Splenic infarcts can occur secondary to thromboembolic disease,
arteritis, myeloproliferative disease, pancreatitis, and sickle
cell anemia. Not all splenic infarcts appear as the classic
wedge-shaped sharply marginated lesions described in the
literature. They can also appear as multiple, poorly marginated
lesions indistinguishable from the other multiple etiologies of
focal splenic lesions. Patients with sickle cell anemia usually
have repeated episodes of splenic infarction, leading to the
so-called auto-splenectomy syndrome. These same patients can also
develop acute splenic sequestration crisis, which is characterized
by sudden, massive splenic enlargement accompanied by an abrupt
decline in hematocrit levels.
The spleen is not an organ prone to the development of tumors
and this is thought to be mainly due to immunologic factors and its
characteristic blood circulation. Neoplastic lesions of the spleen
can be divided into three main categories: lymphoma, metastases,
and non-lymphomatous primary splenic neoplasms. The spleen usually
is involved secondarily in lymphoma of both the Hodgkin's and
non-Hodgkin's subtypes. Primarylymphomas of the spleen are rare,
making up 1% to 2% of cases of lymphomatous involvement of the
spleen, but the overall prevalence of lymphoma makes this the most
common primary splenic neoplasm. Splenic involvement in lymphoma
can take several forms, including homogenous enlargement, miliary
nodules, multifocal lesions, and a solitary mass. The lesions can
also differ widely in their CT and ultrasound appearances, so the
diagnosis of splenic lymphoma is difficult to make by imaging
alone. Although splenic lymphoma is most often confined by the
splenic capsule, local extension with invasion into adjoining
structures has been reported.
Metastatic lesions in the spleen occur most commonly by
hematogenous spread and are almost always seen only in patients
with widespread carcinoma involving three or more organs. The most
common primary sites of splenic metastases are breast and lung,
although on a percentage basis, melanoma has the highest frequency
of splenic involvement with one series showing 34% of melanoma
patients have splenic metastasis at autopsy.5 Splenic
metastases most frequently appear as multiple nodules, although
diffuse infiltration can occur, making the imaging diagnosis
Neoplasms arising from the mesenchymal components of the spleen
are even more rare. Vascular neoplastic proliferations account for
the majority of these lesions. Included in the spectrum of vascular
proliferations are localized and diffuse hemangiomas, lymphangiomas
and lymphangiomatosis, hemangioendothelioma, Kaposi's sarcoma,
angiosarcoma, and hemangiopericytoma. Fewer than 100 of all these
types of neoplasms of the spleen have been reported in the
literature since Langhans first described a case of primary splenic
angiosarcoma in 1879.6 Hemangiopericytomas are even more
rare with only a handful of cases reported since Jurado first
described this tumor in the spleen.7 The tumor arises in
the pericytes, cells whose function is not well understood, but
seems to be related to the regulation of vessel caliber. Most
hemangiopericytomas occur in the soft tissues of the lower
extremities and pelvis. Approximately 25% occur within the abdomen,
in which case the symptoms depend on the tissue of origin. In
summary, although there are no radiologic findings specific for
primary splenic hemangiopericytoma, it is important to keep in mind
the diversity of pathologic conditions involving the spleen when
encountering a splenic lesion on an imaging study.
- Quinn SF, vanSonnenberg E, Casola G, et al: Interventional
radiology of the spleen. Radiology 161:289-291, 1986.
- Fowler RH: Collective review: Hydatid cysts of the spleen.
Int Abstr Surg 96:105-116, 1953.
- Mittelstaedt CA, Partain CL: Ultrasonic -pathologic
classification of splenic abnormalities: Gray-scale patterns.
Radiology 134:697-705, 1980.
- Nelken N, Ignathius J, Skinner M, et al: Changing spectrum of
splenic abscess: Multicenter study and review of the literature.
Am J Surg 154:27-34, 1987.
- Berge T: Splenic metastasis: Frequencies and patterns. Acta
Pathol Microbiol Scand 82:499-506, 1974.
- Langhans T: Pulsating cavernous neoplasm of spleen with
metastatic nodules to the liver. Virchows Arch [Pathol
Anat] 75:273-291, 1879.
- Jurado JG, Fuentes FT, Menendez CG, et al: Hemangiopericytorna
of the spleen. Surgery 106:575-577, 1989.