Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

frequent hyalin vascular type and a plasma cell type—although occasionally found is a mixture of both types. Histologic features consist of lymph node hyperplasia and capillary proliferation.

In a rare patient both multicentric Castleman’s disease and primary effusion lymphoma coexist, and presumably lymphoid cells have undergone malignant transformation. Rarely, a high-grade lymphoma develops even in the localized form of Castleman’s disease (49). An association with Kaposi’s sarcoma has been described.

Castleman’s disease occurs in both children and adults. Clinically, it overlaps with some immunologic conditions. Although Castleman’s disease is often considered to be benign, the multicentric type has a poor prognosis. Anemia and hypergammaglobulinemia develop, especially with the plasma cell variety. In many of these patients a malignancy is the major differential consideration. One should keep in mind that a pathologist may not be able to differentiate Castleman’s disease from Hodgkin’s lymphoma on fine-needle aspiration cytology (50), and although imaging defines these tumors, diagnosis is made from biopsy or surgical tissue.

The most common imaging appearance of Castleman’s disease is of a well-defined tumor, enhancing homogeneously when small but becoming heterogeneous with growth due to central necrosis (51). Computed tomography and US of extraperitoneal Castleman’s disease identify a well-defined, highly vascular tumor mimicking a malignancy (52). Some of these tumors develop vascular encasement. An occasional one develops calcifications. Magnetic resonance imaging also readily detects adenopathy.

Whole-body PET imaging in a patient with Castleman’s disease localized FDG to a pelvic tumor identified previously by CT (53); uptake was less than expected for a lowto intermedi- ate-grade lymphoma.

Surgical resection of unicentric Castleman’s disease tends to be curative. Clinical and biochemical abnormalities clear after tumor resection.

An example: Computed tomography and MRI identified hydronephrosis and a tumor adjacent to the right ureter in a 45-year-old woman; a right nephrectomy was performed for a presumed primary ureteral tumor, but histology revealed plasma cell type of Castleman’s disease

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(54). A year later CT revealed left hydronephrosis and a tumor adjacent to the ureter; steroid therapy was instituted for presumed Castleman’s disease and the tumor resolved.

Necrotizing Lymphadenitis

(Kikuchi-Fujimoto Disease)

Necrotizing lymphadenitis, also called histiocytic necrotizing lymphadenitis, apoptotic lymphadenitis, and Kikuchi-Fujimoto disease, develops mostly in young women and usually resolves spontaneously. Fever and lymphadenopathy are the usual clinical findings. Head and neck adenopathy is most common, but some develop retroperitoneal involvement or splenomegaly. Lymph node infiltration by histiocytes and plasma cells in a setting of lymph node necrosis is a common feature, albeit necrosis is not always found. It is a disease of unknown etiology; a hyperimmune reaction to a possible viral infection has been both suggested and denied. Two women developed necrotizing lymphadenitis during remission of diffuse large B-cell lymphoma (55). Necrotizing lymphadenitis and systemic lupus erythematosus have developed in the same patient. In fact, a type of necrotizing lymphadenitis does exist in lupus, and some type of relationship between the two entities would not be surprising.

Imaging identifies adenopathy, either focal or diffuse. Computed tomography and MR in three patients showed uniformly enhancing small lymph nodes in the submandibular, axillary, gastrohepatic, celiac, periportal, paraaortic, retrocrural, mesenteric, and inguinal regions (56); the lymph nodes were <18mm in diameter.

The differential diagnosis includes infections such as toxoplasmosis and tuberculosis, Castleman’s disease, and malignant lymphoma.

Lymphoma

Clinical

The World Health Organization in 1997 classified lymphomas based on clinical, morphologic, immunologic, and genetic grounds. Lymphomas are subdivided into B-cell neoplasms, T-cell neoplasms, and Hodgkin’s disease. Both B-cell and T-cell neoplasms are further subdivided into precursor neoplasms

PERITONEUM, MESENTERY, AND EXTRAPERITONEAL SOFT TISSUES

and peripheral neoplasms. Peripheral T-cell neoplasms can be further subdivided into disseminated, primary extranodal, and predominantly nodal. Location and clinical syndrome aid in further defining T-cell lymphoma.

The human herpesvirus type 8 (HHV-8 or Kaposi’s sarcoma–associated herpesvirus) is associated with primary effusion lymphoma (or body cavity lymphoma) and multicentric Castleman’s disease. This virus may also have a role in other lymphomas, including multiple myeloma and some atypical lymphoproliferations, and in sarcoidosis, although the evidence is not firm.

Primarily splenic and extraperitoneal involvement is a hallmark of Hodgkin’s lymphoma. The vast majority of primary extranodal lymphomas are non-Hodgkin’s; they involve the extraperitoneum, bowel, mesentery, and other adjacent structures. Lymphomatous omental infiltration is uncommon, with most omental involvement being with non-Hodgkin’s lymphoma. Malignant nodal lymphoma prognosis and therapy differ from bowel lymphoma. With the exception of mucosa-associated lymphoid tissue (MALT) lymphomas, most nonHodgkin’s lymphomas are highly malignant.

Abdominal pain is a common presentation. Diffuse infiltration evolving into bowel obstruction and perforation can lead to an initial presentation of an acute abdomen.

The principal therapeutic options with diffuse lymphoma are chemotherapy and radiotherapy. Chemotherapy combined with autologous hematopoietic stem cell infusion improves patient survival in those with relapsing highgrade non-Hodgkin’s lymphoma. Considerable current research involves the use of antibodies against lymphoma cells.

Imaging

With clinically suspected lymphoma, lymphangiography has been replaced by CT. Numerous studies show that the ability to detect abnormal extraperitoneal lymph nodes is roughly comparable between lymphangiography and CT, but CT has the advantage of also imaging intraperitoneal and other lymph nodes not normally opacified during lymphangiography. Especially with non-Hodgkin’s lymphoma and its high propensity for mesenteric nodal involvement, CT has obvious advantages. Although in the

United States CT has also evolved as the dominant imaging modality with Hodgkin’s lymphoma, the advantages of CT over lymphangiography in this setting are not as clearcut, and lymphangiography continues to be performed for Hodgkin’s lymphoma more often in parts of Europe. Because lymphangiography can suggest tumor infiltration even in normalsized nodes, the presence of supradiaphragmatic Hodgkin’s lymphoma and a normal abdominal CT is considered in some European centers to be an indication for staging lymphangiography. For an adequate nodal evaluation, however, a technically excellent lymphangiogram is necessary, and appropriate skill in performing these studies is not available in all centers. Also, mild adenopathy and node foaminess do not imply lymphomatous involvement and are seen in a number of nonneoplastic conditions. In any case, staging laparotomy has made a discussion of the relative merits of CT and lymphangiography a moot point in most patients. Although more invasive than lymphangiography, laparotomy staging is considered to be more accurate.

The role of lymphoscintigraphy is still debated. Such scintigraphic agents as Tc-99m– diethylenetriamine pentaacetic acid (DTPA)– human serum albumin show promise in lymphoma staging.

Abdominal lymphomas range from nodular to bulky confluent tumors. Mesenteric nodal involvement is considerably more common with non-Hodgkin’s lymphoma than with Hodgkin’s lymphoma. Nodal involvement is seen as numerous smooth soft tissue tumors within the mesentery. Extensive nodal involvement results in confluent mesenteric masses surrounding major vessels (Figs. 14.14 and 14.15). Lymphomas tend to have a homogeneous CT density. With the exception of melanoma, carcinomatosis more often leads to a diffuse mesenteric infiltrate. A rare lymphoma involves the peritoneal surfaces diffusely; it is indistinguishable from carcinomatosis.

Most calcifications in a setting of lymphoma develop after therapy, although a rare untreated Burkitt’s lymphoma contains calcifications.

Ultrasonography has a limited role in lymphoma detection. Tumor involvement ranges from diffuse and nodular to large confluent masses. Involved nodes are homogeneous and mostly hypoechoic in appearance.

Computed tomography is often used to follow a patient with prior lymphoma, with MR being a viable alternative. Yet among 78 patients with stages I to III of follicular lymphoma who relapsed, only 14% of recurrences were detected primarily with abdominal or pelvic CT, with clinical, hematologic, and other imaging detecting the rest (57).

Magnetic resonance imaging in initial tumor detection and staging is still evolving. It has established its usefulness during the first 6 months after therapy in following the tumor size, but the signal intensity patterns during this time are not specific for identifying recurrence. However, MRI does differentiate late posttherapy fibrosis (hypointense on T2weighted images) from viable lymph nodes

(hyperintense or heterogeneous on T2-weighted images). Also, fibrotic tissue shows minimal MR enhancement postcontrast, while recurrence generally enhances markedly. Such lymph node enhancement is not limited to lymphoma; many benign conditions and nodal metastases also enhance.

An exception to the use of CT or MR is in patients who have undergone a prior lymphangiogram, where conventional radiography is often sufficient to visualize any change in opacified nodes.

Biopsy, regardless of how it is obtained, is generally diagnostic. Fine-needle aspiration cytology, although usually diagnostic, occasionally cannot distinguish reactive lymphoid hyperplasia from malignant lymphoma.

PERITONEUM, MESENTERY, AND EXTRAPERITONEAL SOFT TISSUES

Some involved lymph nodes do not revert to normal size after successful therapy. In addition, considerable distortion is produced by fibrosis. Magnetic resonance is helpful in this setting; fibrosis is hypointense on both T1and T2-weighted images. This issue is not always clear-cut, because not only neoplasms but also inflammation and necrosis have an increased signal intensity on T2-weighted images.

Gallium-67 scintigraphy is useful in staging and evaluating lymphoma therapy for both Hodgkin’s disease and non-Hodgkin’s lymphoma. Viable lymphoma tissue takes up Ga 67, a finding not seen with residual fibrosis or necrotic tissue, and an abnormal uptake of Ga-67 citrate after chemotherapy generally implies residual tumor. Nevertheless, Ga 67 has a relatively low sensitivity with low-grade lymphoma.

2-[18F]-fluoro-deoxy-D-glucose PET is highly sensitive in detecting viable tumor and is superior to both CT and Ga-67 scintigraphy. Computer tomography, however, provides additional information, including localization, and thus the current interest in combined PET-CT units. Of note is that PET-FDG detects both Hodgkin’s and non-Hodgkin’s lymphomas but does not differentiate between them. It has a low sensitivity in detecting MALT lymphomas. In general, tumor-to-background activity is greatest with high-grade lymphomas. It detects even normal-sized involved lymph nodes, and PET detects both nodal and extranodal involvement, although the sensitivity appears to be lower for bone marrow involvement than for other sites. False-positive findings occur with some nodes affected by inflammatory disease. The reverse is also true—inflammation may obscure tumor involvement because of increased uptake. The current primary role of FDG-PET is in evaluating residual deformity after therapy by accumulating FDG in viable tumors but not in fibrosis, a task not suitable for CT.

Plasmacytoma

An extramedullary plasmacytoma can occur as an isolated manifestation; it can be a metastasis from another site, or evolve into generalized disease (i.e., multiple myeloma). Most extramedullary plasmacytomas occur in lymph nodes. The diagnosis is often unsuspected prior to cytology.

The most common CT finding is that of a hypodense tumor with little contrast enhancement. Preand postcontrast T1-weighted MR combined with fast spin echo (FSE) short-time inversion recovery (STIR) sequences should detect both focal bone marrow plasmocytomas and diffuse infiltration.

Lymphangioleiomyomatosis

Lymphangioleiomyomatosis is a rare condition difficult to classify, but probably of hamartomatous origin. It consists of smooth muscle proliferation within lymphatics. A single lymphangioleiomyoma is less common than lymphangioleiomyomatosis. The mediastinum, lungs (pulmonary cysts), and retroperitoneum are most often involved, less often the kidneys and other structures. It is related to tuberous sclerosis; in fact, one of the gene mutations found in tuberous sclerosis is also common in lymphangioleiomyomatosis. Pulmonary lymphangioleiomyomatosis tends to be associated with renal angiomyolipomas and, less often, with abdominal lymphangioleiomyomatosis. Some endothelium-lined lymphangiomas (discussed in a previous section) and lymphangioleiomyomas have a similar imaging appearance, with the difference being that the former contains no smooth muscle cells—a finding established by histology. Their etiologies also appear to differ. Abdominal lymphangioleiomyomatosis is due to proliferation of lymphatic smooth muscle cells and the resultant lymphatic obstruction. Most occur in women of childbearing age, with only an occasional lymphangioleiomyoma described in a young child.

In patients with thoracic lymphangioleiomyomatosis, renal angiomyolipomas were found in 54%, abdominal lymphadenopathy in 39%, lymphangiomyomas in 16%, ascites in 10%, a dilated thoracic duct in 9%, and hepatic angiomyolipomas in 4% (58); a direct correlation existed between abdominal lymphadenopathy and the severity of lung disease.

Imaging detects solid or cystic tumors, mostly in the retroperitoneum. Associated lymph node enlargement is common. Of interest is that some of these lymph nodes are hypodense and contain lymph, while others enhance postcontrast, presumably secondary to their mostly smooth muscle content.

Inflammatory Pseudotumor (Fibrosarcoma)

An unusual entity is the so-called inflammatory pseudotumor or fibrosarcoma, a condition believed to be nonneoplastic by some.A number of terms are used in the literature to describe this condition (Table 14.3) and they reflect divergent views held among pathologists about its pathogenesis. Whether the tumors described represent one entity or are a collection of several conditions, are histogenetically related or not, inflammatory or neoplastic, benign or malignant, is conjecture. These tumors were first described in the lungs but they occur throughout the body, including bowel, mesentery, liver, and extraperitoneum. Histologically they consist of fibroblasts, myofibroblasts, variable amounts of fibrosis, and occasional calcifications, and include an inflammatory infiltrate consisting of lymphocytes, plasma cells, and eosinophils. Myofibroblasts appear to play a central role, hence the inclusion of this term in some of the nomenclature. These tumors differ from granular cell myoblastomas, which are considered to be of neural origin. They also differ from xanthogranulomatosis (discussed earlier; see Diffuse Infiltration).

Pathologically, these tumors exhibit considerable heterogeneity, and a diagnosis from a needle biopsy specimen is difficult; immunohistologic studies are often not helpful. They tend to have benign-appearing cytology and often have relative hypocellularity. Clonal chromosomal aberrations have been detected in some, suggesting a malignant tendency. Polymerase chain reaction studies for Epstein-Barr virus and cytomegalovirus suggest that these viruses do not play a role in this entity.

Table 14.3. Alternate terms used for inflammatory pseudotumor (these do not necessarily represent a single pathologic entity)

Fibrosarcoma

Plasma cell granuloma

Inflammatory myofibroblastic tumor

Inflammatory myofibrohistiocytic proliferation

Xanthoma

Fibroxanthoma

Histiocytoma

Plasmacytoma

Solitary mast cell tumor

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Most of these tumors occur in children, but they range from neonates to elderly. Clinically, patients present with pain, anemia, a palpable tumor, or bowel obstruction. Many initially manifest an indolent clinical course and an aberrant response to tissue injury is postulated as a likely pathogenesis. Others, however, act in a malignant fashion. Recurrence is common unless widely excised. Metastases have been reported.

Primary Carcinoma

An unusual entity called normal-sized ovary carcinoma syndrome, primary papillary serous peritoneal carcinoma and other similar names, consists of diffuse malignant abdominal cavity involvement, normal size ovaries, and no obvious source for a primary malignancy found by either preoperative or operative evaluation. In general, distinguishing primary peritoneal tumors such as malignant mesotheliomas and serous surface papillary adenocarcinomas from metastatic peritoneal tumors is a challenge and involves the use of a hyaluronidase digestion test, electron microscopy, and immunohistochemical antibody studies. Comparing women with primary peritoneal carcinoma with those with primary epithelial ovarian cancer reveals very similar findings.

Ascites is common. Peritoneal involvement is either nodular or diffuse (omental cake). The omentum is affected in most, but adenopathy develops only in a minority. An occasional peritoneal primary papillary serous carcinoma contains calcifications.

These rare primary peritoneal adenocarcinomas are a diagnosis of exclusion. In most patients an adenocarcinoma of unknown primary poses a diagnostic and therapeutic dilemma. In general, the yield from multiple diagnostic procedures aimed at detecting the primary site is low and, even if detected, the therapeutic options are limited. One exception to such a nihilistic approach is in those women presenting with malignant ascites and no pelvic tumor, but who are found to have a peritoneal serous papillary adenocarcinoma. Some of these tumors consist of numerous small nodules throughout the peritoneal cavity, at times beyond the resolution of imaging. A number of these tumors respond to chemotherapy and