Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

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those with aneuploid tumors have a much better survival.

Percutaneous biopsy using 15or 16-gauge core biopsy needles provides an alternate approach to open biopsy in children with advanced neuroblastoma. Percutaneous biopsy provides both a histologic diagnosis and enough sample for prognosis.

Imaging

Depending on the site of origin, imaging reveals a suprarenal or paraspinal tumor. Neuroblastomas are poorly encapsulated and compress or invade adjacent structures; aortic or inferior vena caval encasement is often found with larger tumors. In adults, ganglioneuromas tend to surround major blood vessels but do not narrow the lumen. Tumor hemorrhage and necrosis result in a heterogeneous imaging appearance. An occasional neuroblastoma contains a cystic component. Coarse, mottled calcifications are common. They have less CT contrast enhancement than muscle and, similar to neuroblastomas, a heterogeneous, predominantly hyperintense signal is evident on T2weighted MR images. Computed tomography and MRI are preferred over US because of their ability to better image metastases. Bone scans and chest radiographs are obtained preoperatively to detect metastases and establish a baseline.

Gray-scale 2D and 3D US using tissue harmonic imaging identified an adrenal ganglioneuroblastoma in a pregnant woman as an inhomogeneous,encapsulated,solid tumor (38); color and power Doppler showed extensive neovascularity.

Iodine-123-MIBG scintigraphy detects most neuroblastomas but some bone metastases show little or no MIBG uptake (39). SPECT imaging detects more tumors and better defines their location. Both 24-hour and delayed 48hour scanning appear useful; washout can result in some lesions being missed on delayed scans. Occasionally technetium-99m (Tc-99m)– hydroxymethylene diphosphonate (HMDP) bone scintigraphy is positive in an adrenal neuroblastoma.

Although MIBG scintigraphy appears superior to FDG-PET, the latter does detect most

ADVANCED IMAGING OF THE ABDOMEN

primary neuroblastoma foci and metastases. Also, occasionally FDG-PET is positive when a neuroblastoma fails to accumulate MIBG. PET scanning using carbon-11-hydroxyephedrine (HED) will also locate neuroblastomas.

Combined MIBG scintigraphy and MR imaging achieves a better diagnosis of neuroblastoma foci in children than either study individually. A retrospective study found MIBG scintigraphy, MRI and combined MIBG-MRI sensitivities of 69%, 86% and 99% and specificities of 85%, 77% and 95%, respectively (39).

In a newly discovered tumor the differential often includes a Wilms’ tumor. Imaging shows most neuroblastomas to be more inhomogeneous than a Wilms’ tumor. the latter is intrarenal in location, while an adrenal neuroblastoma displaces the kidney inferolaterally. Some paraspinal neuroblastomas extend into the spinal canal, a finding not seen with Wilms’ tumors. At times an adrenal hemorrhage (hematoma) mimics a neuroblastoma. After the initial presentation, US should distinguish an anechoic and avascular hemorrhage from the hyperechoic and vascular neuroblastoma.

Lymphoma

Primary adrenal lymphoma is rare (40). More common is lymphomatous adrenal involvement from adjacent extraperitoneal lymph nodes, either unilateral or bilateral. Clinically silent adrenal involvement is relatively common with the latter, but adrenocortical insufficiency is a late finding with bilateral adrenal involvement.

Imaging findings range from solid nodules to diffuse homogeneous tumors. Adjacent lymphadenopathy is common. Often the adrenal glands are simply replaced by lymphomatous tissue and appear enlarged while maintaining their usual shape. With growth, lymphomas tend to become heterogeneous in appearance. They are hypoechoic with US. Magnetic resonance imaging reveals a signal intensity similar to that of metastases. Increasing enhancement on delayed postcontrast images is typical.

Necrosis and calcifications develop after therapy.

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Less Common Tumors

Rarer adrenal tumors include a bronchogenic cyst, pure lipoma, teratoma, vascular leiomyomas, schwannoma, and even a sarcoma. Occasionally a patient with von Recklinghausen’s disease develops bilateral adrenal neurofibromas, although in this disease adrenal pheochromocytomas are more common. Ectopic tissue is occasionally detected in the adrenal glands (i.e., a choristoma), the most common one being ectopic thyroid tissue (41). Except for the latter, no imaging findings suggest a specific diagnosis.

Hemangioma

Adrenal hemangiomas are rare. Some contain calcifications and often are large. The more typical ones have imaging characteristics similar to those of liver hemangiomas. An occasional adrenal hemangioma contains a central stellate hypointense region on MRI. Hemorrhage and necrosis are relatively common, and these influence their imaging appearance. The gradual tumor enhancement from the periphery inward is not seen as often as with liver hemangiomas. An occasional one presents with extraperitoneal hemorrhage.

An adrenal hemangioma-like appearance in an infant should suggest a hemangioendothelioma. Their imaging appearance is similar to those in the liver.

sisted either of an isolated adrenal myelolipoma (identified by fat evident at CT) or myelolipomatous tissue within other adrenal tumors (consisting of smaller foci containing less fat but more calcifications) (43); larger myelolipomas contained hemorrhage and necrosis. About 20% of these tumors contain small foci of calcifications.

Unenhanced CT should detect most of these tumors. The amount of fat present varies considerably, but a myelolipoma should not contain only fat; a mixture of fat and nonfatty tissue often results in a heterogeneous appearance (Fig. 16.7). Bleeding can obliterate surrounding fat planes (Fig. 16.8). Contrast-enhanced CT can obscure the fat component and miss a tumor.

Ultrasonography shows a highly echogenic tumor.

Magnetic resonance imaging reveals a variable signal with both T1and T2-weighted sequences (Fig. 16.9). The signal decreases with fat suppression. These tumors enhance postcontrast. Their MR characteristics are modified by any hemorrhage and necrosis.

As already mentioned, other adrenal tumors, including a rare adenocarcinoma, contain fat. Differential diagnosis for a fat-containing adrenal lesion also includes a teratoma and liposarcoma. Some cysts contain a fatty component.

A biopsy should be diagnostic. Unless symptoms ensue, most of these tumors can be followed conservatively. With time, they can increase, decrease, or remain unchanged.

Myelolipoma

Adrenal cortical myelolipomas are rare, benign, nonfunctioning tumors composed of fat and bone marrow tissue. They occur bilaterally. Most myelolipomas are small and are discovered incidentally in asymptomatic patients. Anecdotal reports describe extraadrenal perirenal myelolipomas (42). An occasional patient presents with acute pain secondary to intratumoral or extraperitoneal bleeding.

In a minority of patients a myelolipoma is associated with some type of endocrine

Adrenal myelolipomatous tissue reported from the Armed Forces Institute of Pathology con-

Hemorrhage/Hematoma

Some of the more common conditions associated with adrenal hemorrhage are listed in Table 16.2. Usually a hematoma is limited to the adrenal glands, without involving adjacent extraperitoneal tissues.

Adrenal hematomas have an imaging appearance similar to that of hematomas at other locations; their appearance changes and evolves with time.

Neonates

Most adrenal hemorrhage in neonates is idiopathic, although birth stress and related factors

are implicated. Jaundice may be present. Hemorrhage is more common on the right side, except if associated with renal vein thrombosis when it occurs much more often on the left. With an inferior vena cava thrombus hemorrhage tends to be bilateral.

Figure 16.8. Bleeding adrenal myelolipoma. Contrastenhanced CT reveals a fat-containing tumor superior to the right kidney (arrows). Angiography performed shortly after this study identified a hypovascular tumor. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

Typically, these neonates do not develop adrenal insufficiency. A scrotal hematoma is occasionally the initial presentation of adrenal hemorrhage in neonates.

The primary differential diagnosis in a neonate is a neuroblastoma, although MRI will differentiate these, with the exception of a hemorrhagic, cystic-appearing neuroblastoma (see also the description in Neuroblastoma/ Ganglioneuroma, above). Also, hemorrhage should change its appearance over time, become anechoic, and decrease in size. Neonatal adrenal hemorrhage should also be differentiated from adrenal congestion, which develops in perinatal asphyxia and other perinatal stress conditions. Ultrasonography in the latter identifies diffuse adrenal enlargement, a smooth surface, and loss of the central hyperechoic stripe (44); histology in five neonates who died revealed diffuse sinusoidal congestion.

Adults

In adults, spontaneous adrenal hemorrhage ranges from unilateral to bilateral. Aside from trauma, most are associated with stress or a severe illness and are more often unilateral. In a setting of anticoagulant therapy a hematoma usually develops early in the course. If associated with a neoplasm, imaging

should detect tumor enhancement. Adrenal hemorrhage is relatively common in patients with meningococcal sepsis (WaterhouseFriderichsen syndrome); some hemorrhages

Table 16.2. Conditions associated with adrenal hemorrhage

Neonates

Idiopathic

Stress

Renal vein thrombosis

Inferior vena cava thrombosis

Adults Idiopathic Stress

Surgery Hypotension Sepsis

Trauma

Anticoagulant therapy Underlying neoplasm Postpartum period

Meningococcal sepsis (Waterhouse-Friderichsen syndrome)

Primary antiphospholipid syndrome Adrenal vein thrombosis

Inferior vena cava thrombosis

Vasculitis leading to hypercoagulable state and venous thrombosis

Associated with liver transplantation Adrenomyeloneuropathy

extend into adjacent extraperitoneal tissues. In some patients with primary antiphospholipid syndrome hemorrhage is probably due to adrenal vein thrombosis. A right adrenal hemorrhage is a complication of liver transplantation, a not surprising finding because these patients undergo inferior vena caval division and ligation of right adrenal veins.

Imaging findings of adrenal hemorrhage are varied and consist of either unilateral or bilateral gland enlargement, at times asymmetrical, or a focal tumor. A typical CT appearance is a heterogeneous tumor having a density of 50 to 90HU. Some hemorrhages are associated with periadrenal fat infiltration or even involve adjacent diaphragmatic crus. They are hyperintense on both T1and T2-weighted MR images. A hematoma shows no contrast enhancement with either CT or MRI. Angiography, although rarely performed, identifies a hypovascular tumor. With time, the involved gland shrinks and the hematoma decreases in density.

While unilateral hemorrhage generally has few sequelae, bilateral involvement can result in adrenal insufficiency. In either case, an adrenal hemorrhage should be followed until resolution to exclude an underlying neoplasm. With time, some involved glands atrophy and calcify. Presumably in some adults adrenal calcifications represent sequelae of neonatal hemorrhage. The

hallmark of a remote hemorrhage is an extensively calcified gland with no significant soft tissue component. Prior granulomatous disease usually results in more patchy calcifications.

ADVANCED IMAGING OF THE ABDOMEN

Adrenal vein thrombosis can develop in a setting of heparin-induced thrombocytopenia (45).

Insufficiency

Most of the adrenal cortex must be destroyed before adrenal insufficiency (Addison’s disease) manifests clinically. Most often insufficiency is idiopathic, although an autoimmune disorder is often suspected. Other less common etiologies include adrenal hemorrhage, tuberculosis, histoplasmosis, rare adrenal involvement by North American blastomycosis, and sarcoidosis. Infiltration by lymphoma or metastatic carcinoma, when extensive, can also lead to adrenal insufficiency.

In an acute setting of shock, adrenal insufficiency should be considered if CT reveals bilateral, enlarged, hematoma-density adrenal glands. In a setting of septicemia, however, shock may be induced by septicemia rather than adrenal insufficiency. Also, at times adrenal gland enlargement in the face of adrenal insufficiency is due to tumors such as lymphoma or metastases.

Imaging in patients with more chronic adrenal insufficiency shows that about half have bilateral adrenal enlargement, at times containing regions of necrosis and calcification. Enlarged glands tend to decrease in size after appropriate therapy. Some patients have calcified, atrophic glands. Noncalcified atrophic glands are difficult to visualize with imaging.

Iron deposition in the adrenal glands in patients with hemochromatosis eventually results in mild adrenal insufficiency. Computed tomography reveals small glands having increased attenuation.

Vascular Lesions

An aneurysm of an adrenal artery is rare; rupture leads to a periadrenal hematoma. Imaging reveals a cystic tumor, hematoma, and possible thrombus in the artery. These aneurysms can be diagnosed by angiography and are amenable to embolization.

Immunosuppression

Both fungal and viral adrenal infections are more common in AIDS patients than in the general population. Sufficient gland destruction results in adrenal insufficiency.

Lymphoma predominates among adrenal tumors in AIDS patients. Kaposi’s sarcoma is less common. Several adrenal adenocarcinomas have been reported, although the association may be fortuitous.

Postoperative Changes

An adrenalectomy is performed using either an open or laparoscopic approach and either an anterior, posterior, or a thoracoabdominal incision. A transthoracic approach is preferred by some. Using anterior transabdominal approach the left adrenal gland is reached by either mobilizing the spleen and pancreatic tail, or using the lesser sac as a pathway and displacing the pancreas away from the adrenal gland. An open adrenalectomy is generally performed in patients with a suspected malignancy and for tumors larger than about 6cm. A laparoscopic adrenalectomy is considered for others; it requires minimal access, is least painful to the patient, and results in a shorter hospitalization than an anterior approach.

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