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DOI:10.2214/AJR.08.1011
AJR 2008; 191:1477-1479
© American Roentgen Ray Society

Radiologic–Pathologic Conferences of the University of Rochester School of Medicine

Radiologic–Pathologic Conferences of the University of Rochester School of Medicine: Inflammatory Pseudotumor of the Spleen

Shweta Bhatt1, Rochelle Simon2 and Vikram S. Dogra1

1 Department of Imaging Sciences, University of Rochester School of Medicine, 601 Elmwood Ave., Box 648, Rochester, NY 14642.
2 Department of Pathology, University of Rochester School of Medicine, Rochester, NY.

Received April 3, 2008; accepted after revision May 29, 2008.

Address correspondence to V. S. Dogra (vikram_dogra{at}urmc.rochester.edu).

Keywords: CT • histopathology • inflammatory pseudotumor • MRI • spleen

Inflammatory pseudotumor of the spleen is an uncommon benign entity with debated etiology that is characterized by a mixture of inflammatory cells and a component of myofibroblastic spindle cells. This entity was first described by Cotelingam and Jaffe in 1984 [1].

Splenic inflammatory pseudotumors are most frequently detected incidentally. The diagnosis in all reported cases was made after splenectomy because of the imaging resemblance of inflammatory pseudotumor to malignant tumors of the spleen.

Our patient was a 31-year-old man who, while being evaluated for acute appendicitis, was found to have a hypodense splenic lesion. He had no significant history. Contrast-enhanced CT showed an enhancing splenic lesion measuring 5.3 x 3.8 x 4.8 cm (Figs. 1A and 1B). A differential diagnosis of atypical hemangioma, lymphoma, and hamartoma was considered, and MRI was performed to further characterize the lesion. MRI was not very helpful (Figs. 1C and 1D) and the patient underwent splenectomy.


Figure 1
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  		Fig. 1A —31-year-old man with inflammatory pseudotumor of spleen. Contrast-enhanced axial CT scan in portal venous phase shows well-circumscribed splenic lesion measuring 5.3 x 3.8 x 4.8 cm with central calcification and peripheral uniform enhancement.

 

Figure 2
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  		Fig. 1B —31-year-old man with inflammatory pseudotumor of spleen. Lesion shows complete filling with contrast materialon delayed CT image.

 

Figure 3
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  		Fig. 1C —31-year-old man with inflammatory pseudotumor of spleen. Fast multiplanar spoiled gradient-echo T1-weighted image (TR/TE, 215/1.6) in axial plane shows well-circumscribed splenic lesion that is almost isointense to splenic parenchyma.

 

Figure 4
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  		Fig. 1D —31-year-old man with inflammatory pseudotumor of spleen. Lesion has low signal intensity on T2-weighted single shot fast spin-echo sequence (94,285/463).

 
Radiologic Features

Unenhanced CT showed a well-circumscribed solitary low-attenuation mass with or without calcification. The size of these lesions can range from 3.5 to 22 cm in diameter, with most larger than 10 cm. Contrast-enhanced images show early enhancement and a gradual filling of the lesion on delayed phase imaging [2]. The presence of a central satellite area corresponding to fibrous plaque on CT examination after administration of a contrast agent strongly suggests an inflammatory pseudotumor [3].

On MRI, these lesions are hypo- to iso-intense to the surrounding spleen on T1-weighted images and hyperintense on T2-weighted images. After IV contrast administration, there is inhomogeneous delayed enhancement similar to that observed on CT.

Inflammatory pseudotumors appear as well-circumscribed, hypoechoic masses on sonography. Radiologic findings can rarely lead to a definitive diagnosis because many other splenic neoplasms are similar in appearance. Other splenic neoplasms that mimic splenic inflammatory pseudotumor include lymphoma, metastatic carcinoma, splenic hamartoma, and hemangioma [4, 5].

Pathologic Features

A definitive diagnosis of splenic inflammatory pseudotumor can be made at pathology only after a splenectomy, which is usually performed because of the concern for malignancy. Inflammatory pseudotumor of the spleen, or inflammatory myofibroblastic tumor, is usually a solitary lesion that may be multinodular. The cut surface tends to have a variegated color due to necrosis, hemorrhage, and cellular infiltration (Fig. 1E). Microscopically, the lesion is composed of spindle cells and intermixed inflammatory cells, including plasma cells, lymphocytes, and histiocytes (Figs. 1F and 1G). The dominant growth pattern may be compact spindle cells, collagenous stroma, or xanthogranulomatous. The spindle cells show smooth-muscle differentiation and are generally positive for the immunohistochemical marker smooth-muscle actin, whereas the interspersed histiocytes may be highlighted by the presence of CD68. The plasma cells are polyclonal, ruling out a plasma cell neoplasm [6].


Figure 5
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  		Fig. 1E —31-year-old man with inflammatory pseudotumor of spleen. After splenectomy, cut surface of corresponding gross specimen shows well-circumscribed inflammatory pseudotumor in spleen.

 

Figure 6
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  		Fig. 1F —31-year-old man with inflammatory pseudotumor of spleen. Low-magnification photomicrograph of normal spleen shows red (R) and white (W) pulp on left adjacent to inflammatory pseudotumor (T) on right. (H and E, x100)

 

Figure 7
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  		Fig. 1G —31-year-old man with inflammatory pseudotumor of spleen. Higher-magnification photomicrograph shows spindle cells (arrows) and large, spindled and ovoid, angulated vesicular nuclei. Note background of sclerosis with heavy mixed inflammatory infiltrate of lymphocytes and small round dark nuclei, plasma cells (arrowheads), and occasional eosinophils. (H and E, x400)

 

Conclusion

Splenic inflammatory pseudotumor, although a pathologic diagnosis, should be considered in the differential diagnosis of a hypoattenuating nodule in the spleen, particularly in the presence of a central scar and delayed enhancement on contrast-enhanced images.

References

  1. Cotelingam JD, Jaffe ES. Inflammatory pseudotumor of the spleen. Am J Surg Pathol 1984;8 : 375–380[Medline]
  2. Rabushka LS, Kawashima A, Fishman EK. Imaging of the spleen: CT with supplemental MR examination. RadioGraphics1994; 14:307 –332[Abstract]
  3. Franquet T, Montes M, Aizcorbe M, Barberena J, Ruiz De Azua Y, Cobo F. Inflammatory pseudotumor of the spleen: ultrasound and computed tomographic findings. Gastrointest Radiol 1989;14 : 181–183[CrossRef][Medline]
  4. Hayasaka K, Soeda S, Hirayama M, Tanaka Y. Inflammatory pseudotumor of the spleen: US and MRI findings. Radiat Med1998; 16:47 –50[Medline]
  5. Yan J, Peng C, Yang W, et al. Inflammatory pseudotumour of the spleen: report of 2 cases and literature review. Can J Surg 2008; 51:75 –76[Medline]
  6. Neuhauser TS, Derringer GA, Thompson LD, et al. Splenic inflammatory myofibroblastic tumor (inflammatory pseudotumor): a clinicopathologic and immunophenotypic study of 12 cases. Arch Pathol Lab Med 2001; 125:379 –385[Medline]

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