Errors made in the ultrasound diagnostics of the spleen.

Ultrasonography, like any imaging method, entails the risk of errors. From among all means of imaging, it is the most subjective and dependent on the examiner's knowledge and experience. This paper presents the causes of examiner-dependent errors as well as those which result from technical settings and preparation of the patient for the examination. Moreover, the authors discuss the most frequent errors in the diagnosis of splenic conditions, which result from insufficient knowledge concerning anatomical variants of this organ, wrong measurements and incorrect examination technique. The mistakes made in the differentiation of focal lesions of the spleen and its hilum are also discussed. Additionally, the differentiation of collateral circulation, lymph nodes and accessory spleens is mentioned. The authors also draw attention to erroneous interpretation of the left liver lobe as a fragment of the spleen as well as the prominent tail of the pancreas filled with gastric contents and intestinal loops as abnormal masses or fluid cisterns in the area of the splenic hilum. Furthermore, the pathologies of the hilum are discussed such as tumors of the splenic flexure of the colon, lesions arising from the left kidney or the left adrenal gland. The authors list characteristic imaging features of the most common focal lesions visualized in a standard ultrasound scan as well as enhancement patterns appearing in contrast-enhanced examinations. The article discusses the features and differentiation of, among others, infarction, splenic cysts including hydatid ones, abscesses and angiomas. The ultrasound appearance of lymphoma and secondary involvement of the spleen by other malignant neoplasms is also mentioned. Moreover, the authors provide useful tips connected with imaging techniques and interpretation of the findings. The ultrasound examination carried out in compliance with current standards allows for an optimal assessment of the organ and reduction of the error-making risk. This article is based on the publication of the experts from the Polish Ultrasound Society of 2005 and updated with the latest findings in pertinent literature. The photographic documentation, which provides images of the discussed lesions, is attached to this article.

Introduction

Ultrasound scanning (US) constitutes the initial and primary imaging examination of the spleen. The dynamic technological development in the field of ultrasonography improved the detectability and differentiation of abnormal splenic lesions. Still, however, diagnostic errors are being made. There are numerous causes of such errors. They range from technical aspects (low-quality scanners, wrong settings or presence of artifacts), through patient-related factors (improper preparation for the examination, serious condition or lack of cooperation), to examiner-dependent errors (insufficient knowledge, lack of experience, examination technique inconsistent with the standards, creating and interpreting false images, too brief or superficial examination, inappropriate assessment of other organs after detecting and focusing on one pathology only). Mistakes and errors may also occur due to the lack of access to clinical data and earlier examination results as well as the failure to perform an interview or a physical examination.

Errors related to the examination technique

The examination of the spleen is restricted by its anatomical position. It is located below the left costal margin and surrounded by ribs, stomach, large intestine and costodiaphragmatic recess of the pleura. In addition, the cause of wrong interpretation of images may be the inappropriate preparation of the patient for the examination (large amount of gas in the intestines or lack of cooperation). Each time, it is important to visualize the entire spleen by applying the transducer in the area of the 10th intercostal space in the anterior axillary or midaxillary lines. In the case of splenomegaly, accessing the spleen along the left costal margin is frequently omitted, which may lead to the failure to recognize the subcapsular pathologies(.

Errors related to the assessment of size

Anatomical variants of the spleen, such as polysplenia, prominent poles and persistent fetal lobulation, may constitute a cause of erroneous interpretation of tumors of the left adrenal gland (figs. 1 and 2) or of the left kidney. This error, however, may be avoided by performing a range of longitudinal and transverse scans of the spleen(.

Fig. 1

Two-lobe spleen, erroneously interpreted as a tumor of the left adrenal gland

Fig. 2

The same patient. A different application of the transducer allows for the accurate diagnosis of the two-lobe spleen with a prominent superior pole

Due to the anatomical neighborhood of the spleen and the left liver lobe as well as due to the fact that the hepatic parenchyma usually presents lower echogenicity than the splenic one, the left liver lobe is sometimes incorrectly interpreted as a subcapsular hamatoma of the spleen (fig. 3). This usually happens in slender patients with narrow chest and prominent left liver lobe. The presence of portal vessels within the area erroneously suggesting a “splenic hematoma” constitutes a differentiating factor(.

Fig. 3

Left liver lobe (LP) erroneously interpreted as a subcapsular hematoma of the spleen

When estimating the size of the spleen, examiners frequently measure its length which according to medical textbooks should not exceed 120 mm(. One needs to remember, however, that it is an approximate number since there are no criteria concerning the extent of splenic enlargement. In some patients, minor splenomegaly, e.g. to 130 mm, may be a physiological phenomena (the analysis of the size of the spleen should include the height of the patient). In others, on the other hand, such an enlargement indicates the beginning of disease (developing portal hypertension, lymphoma, generalized and local inflammation or immune system disorders)(. The procedure in such cases must be individualized. The results of the interview,

physical examination as well as the findings of other tests should be taken into account. Doubts may be resolved by another diagnostic examination or US check up. Substantial splenomegaly, when the inferior pole reaches the left wing of the ilium, is most frequently observed in the course of osteomyelofibrosis, primary polycythemia, chronic myeloid leukemia, malaria and leishmaniasis(.

During each scan, examiners should thoroughly examine the splenic hilum where numerous pathological changes may be found. First and foremost, one needs to search for enlarged lymph nodes as well as neoplastic infiltrations in the course of lymphoma and neoplasms of the stomach and pancreas. The prominent tail of the pancreas may be erroneously interpreted as a pathological mass in the splenic hilum. Its oval shape, homogeneous echogenicity and the presence of the splenic vein constitute the differentiating factors(. In the hilum, one may also find a tumor of the splenic flexure of the colon, which in a US examination is usually hypoechoic, but occasionally, its echogenicity may be mixed. The intestinal lumen is narrow and filled with gas. Moreover, the splenic hilum may also show certain lesions arising from the kidney or the lateral limb of the left adrenal gland. Furthermore, if filled, the stomach and intestinal loops create an image of fluid cisterns or pathological masses in the splenic hilum (fig. 4). However, by observing this area for a longer period of time, the examiner may notice peristalsis and a consequent difference in the size of a presumed “lesion” during the examination. When assessing the splenic hilum, one needs to examine the vessels. The differentiation of the collateral vessels, occurring in portal hypertension, and enlarged lymph nodes should not pose problems when color Doppler is used. The image should be interpreted with simultaneous assessment of the remaining abdominal organs.

Fig. 4

Stomach filled with fluid content mimicking a splenic cyst

When diagnosing enlarged lymph nodes, the examiner needs to take into account the presence of accessory spleens. They occur in the splenic hilum in about 0.1–11% of patients. Accessory spleens are most often detected incidentally and they are visualized as single changes with the echogenicity identical to that of the spleen. They are typically located at one third of the lower length of the hilum or in the area of the poles and their diameters range from 10–40 mm. Furthermore, the accessory spleen is characterized by the presence of the capsule, hilum and splenic arterial vascularity(. Unambiguous diagnosis is possible in contrast-enhanced ultrasound examination, scintigraphy or computed tomography (CT).

Errors related to the assessment of focal lesions

The diagnostics of focal lesions in the spleen is problematic due to the low specificity of the US examination. The same image of a focal lesion may be assigned to numerous disease entities and the other way round – one disease entity may give numerous US images. The interpretation of a US image together with the data obtained in the interview, physical examination and results of additional tests, allows for establishing the most probable diagnosis, differentiation and, if needed, suggestion for further examinations of the diagnostic algorithm.

Single and hyperechoic focal lesions usually are benign (angioma, splenoma, Gaucher disease and Niemann-Pick disease). Multiple lesions of low echogenicity especially those which occurred in a short period of time in oncological patients suggest malignant character. Standard US examinations are characterized by low specificity which does not allow for unambiguous differentiation between malignant and benign lesions. CT or magnetic resonance imaging (MRI) are the methods of choice, but ultrasound examination with the use of contrast agents (CEUS) is a highly promising method(. The verification with the use of fineneedle biopsy (FNAB) is conducted rarely, mainly to verify the lesions of metastatic character. However, the risk of complications is similar as in the case of FNAB of other organs(.

Infarction

Infarction is one of the most common focal lesions of the spleen. The infarction area is quite characteristic in the US examination and presents the image of a pyramid with its base turned towards the splenic capsule. In its early phase, the focus of infarction is hypoechoic or anechoic. Later, however, the echogenicity increases. If infarction presents an irregular image and low echogenicity, it requires the differentiation with other focal lesions, above all with the inflammatory ones. Here, two-phase CT or CEUS are recommended. After the administration of the contrast agent, the infarction area remains hypointense in relation to the normal splenic parenchyma in all phases of the examination(. In the case of massive infarction, involving the whole organ, the absence of the enhancement of the spleen in relation to the adjacent organs or structures is observed(. The outcomes of infarction may be: a pseudocyst, splenic abscess or, more rarely, focal fibrosis(.

Cyst

In the determination of the etiology of splenic cysts (inflammatory, post-traumatic, congenital or hydatid), a good doctor-patient interview is the basis. Post-traumatic cysts are the most common. Congenital, post-inflammatory and post-infarction cysts are detected more rarely, but hydatid ones occur seldom and usually are secondary to hydatid cysts of the liver. Hydatid cysts are the only ones that possess vascularized walls. As a result of extravasation of blood to the cystic lumen, hydatid cysts may manifest themselves with acute symptoms (sudden pain in left hypochondriac region, pain on palpation and palpable resistance in this area)(. When the cystic lumen in B-mode examination is not entirely anechoic, one may erroneously diagnose tumors or abscesses. In CT or CEUS, such lesions are not enhanced in any phase of the examination(.

Angioma

The appearance of splenic angiomas is, in most cases, not different from the US appearance of hepatic angiomas. The angiomas in cystic-solid forms (fig. 5) are the most problematic to diagnose. This is because they may resemble a multilocular cyst or metastasis in the cystic form (lymphoma or melanoma)(. In CEUS examinations, angiomas demonstrate peripheral/ring-like enhancement pattern, filling in towards the center in the arterial phase. Some angiomas of, so called, high flow, present homogeneous enhancement of the whole lesion in the arterial phase with gradual decrease of enhancement in the parenchymal and venous phases in relation to the surrounding parenchyma, which hinders their differentiation from a malignant lesion(.

Fig. 5

Cystic-solid angioma of the spleen (arrows)

Tuberculosis

In the case of tuberculosis, the diagnosis is established on the basis of the presence of disseminated hyperechoic areas in the splenic parenchyma or calcifications in combination with the clinical picture. The diagnosis is more complicated when uncharacteristic areas of necrosis are formed in the course of the disease. They resemble classic abscesses. In order to differentiate between them, cytological tests are necessary(.

Abscesses

The clinical picture of the disease and the results of laboratory tests constitute important elements in the differentiation diagnostics between mycotic and bacterial abscesses(. Bacterial abscesses usually have a well-developed and vascularized capsule which allows for their differentiation from primary and metastatic neoplastic lesions. The lumen of the abscess may be completely anechoic or have low, mixed or high echogenicity. In CEUS examinations, abscesses are hypointense in relation to the normal splenic parenchyma and in the delayed phase, only the septations and capsule undergo enhancement(.

Apart from the “wheel-within-a-wheel” or “target” patterns, developed mycotic abscesses present diversified images and thus, are difficult to diagnose. Similarly to benign or malignant neoplasms, they may be solitary or multiple and have high or low echogenicity. Mycotic microabscesses are particularly troublesome. Due to their small sizes (2–4 mm) and scattered character, they must be differentiated from an infiltration of disseminated lymphoma or peliosis. Cytology and mycological tests are frequently nondiagnostic(. Scattered hypoechoic areas may also occur in sarcoidosis (fig. 6).

Fig. 6

Multiple mycotic abscesses and focal lesions in sarcoidosis – two similar appearances

Lymphomas

In various forms of non-Hodgkin lymphoma or in Hodgkin disease, several types of US images may be distinguished which are common for both of these disease entities. The involvement of the splenic parenchyma may manifest itself with slight enlargement of the spleen with homogeneous echogenicity and the presence of solitary or multiple focal lesions. It may also present itself as a diffuse infiltration (fig. 7). In leukemia, the spleen is usually enlarged but its echogenicity remains unchanged.

Fig. 7

Lymphoma in the form of numerous disseminated focal lesions (crosses). The lymph nodes in the splenic hilum are affected (arrows)

The most problematic character differentiation concerns slight, disseminated, hypoechoic, or even anechoic, lesions in the splenic parenchyma, which may constitute microabscesses, mycotic abscesses, metastatic lesions or rarely occurring splenic peliosis (cyst-like dilatation of the splenic sinuses)(. In a CEUS examination, lymphomas and metastatic lesions are characterized by the enhancement in the early phase with subsequent quick contrast wash-out(.

Metastases to the spleen

The appearance of metastases to the spleen is diverse and uncharacteristic. The echogenicity of the majority of tumors is lower that the surrounding parenchyma (but rarely, it might be increased). The echostructure may be heterogeneous with the areas of necrosis, calcifications and cystic-solid lesions. Cystic forms of metastases usually indicate the metastases of carcinomas of the ovary and large intestine. Isolated metastases, on the other hand, observed solely in the spleen originate from ovarian carcinoma (fig. 8 A, B) or melanoma.

Fig. 8 A

Metastases of ovarian carcinoma to the spleen (arrows)

Fig. 8 B

Metastases of ovarian carcinoma to the spleen

Conclusion

The article presented the most commonly made errors in ultrasound examination of the spleen. Such an examination, if performed in accordance with current standards, including the analysis of all available clinical data, in many cases allows for an accurate interpretation of obtained images or, if this is not possible, for the indication of further diagnostic method.