Eur. Radiol. (2001) 11: 509±512 Ó Springer-Verlag 2001

F. J. PØrez Fontµn R. Soler M. Santos I. Facio

P E D IAT R I C

Accessory spleen torsion: US, CT and MR findings

F. J. PØrez Fontµn ( ) ´ R. Soler ´ M. Santos Department of Radiology, Hospital Juan Canalejo, Xubias de Arriba, 84, 15006 La Coruæa, Spain

Abstract Torsion of an accessory spleen is a very unusual entity that can appear with abdominal pain associated with the presence of an avascular mass. We report the case of a 13-year-old boy with torsion and infarction of an accessory spleen presenting as a painful abdominal mass in which imaging examination with US, CT and MR showed a large avascular mass in the upper left abdomen.

I. Facio Department of Radiology, Centro Oncológico, Avda Monserrat, s/n, 15009 La Coruæa, Spain

Key words Spleen ´ Accessory spleen ´ Torsion ´ CT ´ MR ´ Ultrasound

Received: 16 December 1999 Revised: 24 May 2000 Accepted: 24 May 2000

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Introduction Accessory spleen is a congenital anomaly that consists of ectopic splenic tissue separated from the main body of the spleen. The spleen develops from mesenchymal cells that migrate during fetal life into the dorsal mesogastrium and a failure in the fusion of splenic tissue results in the formation of an accessory spleen [1, 2]. The frequency of accessory spleens is 3.1±3.7 % of CT and US examinations [2, 3]; however, the frequency of accessory spleen is difficult to estimate because it is frequently asymptomatic and thus may be unrecognized. Accessory spleens have been found as an incidental finding in 10 % of autopsy series and in 33 % of patients with hematologic diseases [3]. Occasionally, as in our case, accessory spleen may appear with symptoms related to acute or recurrent torsion and infarction [4, 5]. Clinical presentation of torsioned accessory spleen is usually heralded by abdominal pain without any clinical or laboratory clue for the correct diagnosis.

We describe the US, CT and MR examinations of an accessory spleen with torsion and infarction in a teenager with abdominal pain and vomiting.

Case report A 13-year-old male patient with a history of intermittent abdominal pain of 1-month duration was admitted with severe left hypochondrial pain and vomiting. Physical and laboratory examinations were normal. Abdominal plain radiograph showed a soft tissue mass over the left kidney silhouette. A ultrasound examination was performed which revealed a homogeneous oval mass with good sound transmission, measuring 10 cm in diameter (Fig. 1), anterior to the aorta and independent of the kidney, pancreas and spleen; a normal-size spleen could be seen in its normal position. Unenhanced CT scan showed a well-defined soft tissue mass in the upper left abdomen adjacent to the pancreatic tail and clearly separated from the spleen, left kidney and left adrenal gland. The mass was hypodense as compared with the spleen. After i. v. injection of contrast material, the mass remained hypodense with only a thin peripheral rim enhancement (Fig. 2). Magnetic resonance imaging was performed on a 0.5-T unit and showed that the mass was

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Fig. 1 Longitudinal US examination shows a well-defined, homogeneous hypoechogenic mass, anterior to the aorta

Fig. 3 Sagittal T1-weighted image shows a hypointense mass with a thin peripheral hyperintense rim (arrows) situated anterior to the descendent colon. Normal spleen can be seen in the usual location (asterisk)

Discussion

Fig. 2 Contrast-enhanced CT scan of upper abdomen shows an intraperitoneal hypodense mass of 10 cm with a thin peripheral enhanced rim and a small crescent of subcapsular fluid. A clear cleavage plane is seen related to the neighbouring structures

hypointense with a thin peripheral hyperintense halo on T1weighted spin-echo images (TR/TE: 500/15 ms; Fig. 3) and became homogeneously hyperintense on T2-weighted spin-echo (TR/TE: 2000/120 ms) sequences. With the suggested diagnosis of congenital malformation of the gut or mesentery, the patient was operated on and the lesion was resected. Surgical exploration showed a rounded violet mass with a twisted pedicle, located under the omentum, in the vicinity of the colonic splenic flexure. Histological study revealed haemorrhagic and infarcted splenic tissue.

An accessory spleen is caused by the failure of splenic anlage to fuse during embryogenesis [2]. The size varies from a few millimetres up to 1.5±2 cm in diameter [3, 6], but in patients with pathologic splenic findings or in those who have previously undergone splenectomy, accessory spleens can hypertrophy and reach a size of 5 cm or more [2]. Accessory spleens are most often located in the vicinity of the splenic hilum, along the course of the splenic vessels or omentum [6], but they may occur anywhere in the abdomen and even in the left scrotum [2, 4]. The vascular pedicle of an accessory spleen is most commonly related to the splenic hilum but may also be related to the tail of the pancreas, the gastrosplenic ligament, the small bowel mesentery or to vessels from the fundus of the stomach [7]. Although usually accessory spleen appears as an isolated asymptomatic abnormality, it can be associated with other anomalies such as polysplenia and short pancreas [8]. Torsion and infarction of an accessory spleen is a very rare process, with only a few previous reports dealing with the radiological findings [4, 5, 7, 9, 10]. Patients range from infants to the elderly, but more than

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half of the reported cases were children [4]. The symptoms varied from vague abdominal pain in the case of a wandering accessory spleen with intermittent torsion [8], to fever, vomiting and acute onset of severe abdominal pain in case of infarction [4, 5]. The diagnosis is usually established with the aid of imaging. Abdominal plain radiographs may demonstrate a soft tissue mass depending on the size of the lesion. In our case the accessory spleen was very large, reaching 10 cm in diameter, and a mass effect could be seen over the left kidney shadow. We agree with Valls et al. [5] in thinking that probably so large a size of the accessory spleen, in the absence of hematologic or liver disease, can be due to venous congestion secondary to twisting of the vascular pedicle. The ultrasonographic descriptions of previously reported cases include a hypoechoic well-encapsulated oval mass in the left upper quadrant [4], a hypoechoic mass behind the stomach [7], a hypoechoic mass with central hyperechoic areas [9] and a nodular solid mass below the splenic hilus and adjacent to the left kidney [5]. In our case a well-delineated solid mass with good sound transmission could be seen. In all these cases the presence of the main spleen is in its normal position discarding the possibility of a wandering spleen. Doppler ultrasound can be used to evaluate the degree of vascularization of an abdominal mass; however, the absence of flow does not allow differentiation between a cystic mass or an ischaemic lesion such as a twisted accessory spleen. On CT studies accessory spleen tissue tends to exhibit the same pattern of contrast enhancement, as does the spleen itself. In the few reports [4, 5] about a twisted infarcted accessory spleen, and in our case, the CT findings are similar to classical pattern reported in diffuse splenic infarcts. Diffuse infarctions appear on CT as massive hypodense lesions which involve the splenic parenchyma with peripheral enhancement due to arterial supply from capsular vessels [11]. The CT reports of twisted wandering spleen have shown a whirled appearance of the splenic pedicle and surrounding fat at the splenic hilum, hyperdense splenic vessels corresponding to acute thrombosis [12], or ascitis with low attenuation of the pancreatic tail due to necrosis [13]. These findings have not been reported in torsion of an accessory spleen and were not seen in our case perhaps due to the small

size of the vascular supply and independence from the pancreatic tail. The torsion of vascular pedicle produces a spleen infarction which, on CT scan, has considerably lower attenuation compared with normal spleen or liver. When masses with these CT characteristics are found in the abdomen, the differential diagnosis between mesenteric or omental cysts, intestinal duplication, pancreatic pseudocysts and abscesses should be considered [12]. The MR imaging has been reported in two previous cases. In the first case an infarcted accessory spleen presented as a hypointense mass on T1- and T2-weighted images containing low-signal structures which were thought to be due to vessels. Three weeks later, the infarcted accessory spleen showed homogeneous high signal intensity on T2-weighted images, whereas on T1weighted images, the signal intensity remained low except for a peripheral rim of high signal intensity, presumably reflecting a combination of peripheral fibrosis secondary to progressive inflammatory changes superimposed on infarction [4]. In the other case Jans et al. suggested that T2-weighted images may help in the diagnosis of infarcted spleen by demonstrating the presence of haemorrhagic necrosis [10]. In our case MR examination was performed after a month of intermittent abdominal pain and showed findings similar to the previously reported case. Hyperintensity on T1-weighted images is usually related to fat deposit or paramagnetic materials. Because we did not find peripheral adhesions, fibrous tissue or fat deposits in the pathological specimens of our case, we think that the cause of the hyperintense peripheral rim was not related to fibrosis as has been previously stated [4]. We thought that a possible explanation for the peripheral hyperintense rim on T1-weighted spin-echo sequence could be the presence of haemoglobin degradation product methemoglobin related to the evolution of infarcted areas or slow-flowing blood in residual capsular or subcapsular vessels. In conclusion, torsion of an accessory spleen implies a diagnostic problem which derives from the fact that it settles in a normal but inconstant structure. Torsion of an accessory spleen should be considered in the differential diagnosis when an avascular intraperitoneal mass is seen in a patient with acute or subacute abdominal pain.

References 1. Masamune A, Okano T, Satake K, Toyota T (1994) Ultrasonic diagnosis of torsion of the wandering spleen. J Clin Ultrasound 22:126±128

2. Santamaria G, Vilana R, Salvadó E, Clavero JA, Ayuso MC, Luburich P (1992) Bazo accesorio: caracteristícas ultrasonogrµficas y tomogrµficas. Rev Esp Enferm Dig 81:263±266

3. Freeman JL, Jafri SZ, Roberts JL, Mezwa DG, Shirkhoda A (1993) CT of congenital and acquired abnormalities of the spleen. Radiographics 13:597±610

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4. Seo T, Ito T, Watanabe Y, Umeda T (1994) Torsion of an accessory spleen presenting as an acute abdomen with an inflammatory mass. US, CT and MRI findings. Pediatr Radiol 24:532±534 5. Valls C, MonØs L, Gumµ A, López-Calonge E (1998) Torsion of a wandering accessory spleen: CT findings. Abdom Imaging 23:194±195 6. Dodds W, Taylor AJ, Erickson SJ, Stewart ET, Lawson TL (1990) Radiological imaging of splenic anomalies. AJR 155:805±810

BOOK RE VIEW Orrison W. W. Jr. (Editor): Neuroimaging (2 volume set). Philadelphia: WB Saunders, 2000, 1776 pages illustrated, £ 280.00, Set ISBN 0-7216-6799-6 (continued from p. 505) The first chapters of Section 2 concerns normal brain imaging and normal variations of the head. Chapters 19 and 20 deal with intracranial tumours. There is some discrepancy between the chapter on intraaxial tumours (28 pages, 96 references) and the chapter on extraaxial and sellar tumours (106 pages, 718 references). The chapter on cerebrovascular disease is rather poorly referenced. The six remaining chapters of this section include intracranial infection, white matter disease, neurodegenerative disorders, haemorrhage, head trauma and seizure imaging. It is worth mentioning that the chapter on haemorrhage includes a library of illustrative cases.

7. Dahlin LB, Anagnostaki L, Delshammar M, Fork FT, Genell S (1995) Torsion of an accessory spleen in an adult. Eur J Surg 161:607±609 8. Kaniklides C, Wester T, Olsen L (1999) Accessory wandering spleen associated with short pancreas. Acta Radiol 40:104±106 9. Chateil JF, Arboucalot F, Perel Y, Roy D, Vergnes P, Diard F (1996) Torsion aigüe dœne rate accessoire. J Radiol 77:209±211 10. Jans R, Vanslembrouck R, Van Hoe L, Sockx L, Demedts I, Baert AL (1997) Torsion of accessory spleen in a an adult patient: imaging findings at CT, MRI and angiography. J Belge Radiol 80:229±230

11. Balcar I, Seltzer SE, Davis S, Geller S (1984) CT patterns of splenic infarction: a clinical and experimental study. Radiology 151:723±729 12. Raissaki M, Prassopoulos P, Daskalogiannaki M, Magkanas E, Gourtsoyiannis N (1998) Acute abdomen due to torsion of a wandering spleen: CT diagnosis. Eur Radiol 8:1409±1412 13. López MenØndez C, Calvo J, LópezNegrete L, Prieto A, Luyando L (1995) The wandering spleen. Eur J Radiol 21:89±91

Section 3 consists of head and neck, orbit and spine. It remains unclear why chapters on spine imaging are included in this section. It appears logical to dedicate a separate section to spinal imaging in a neuroimaging textbook. The images of Chapters 28 (temporal bone) and 29 (skull base) were taken from the author's digital teaching file. The other chapters concern the orbit, nasal cavity and paranasal sinuses, pharynx and oral cavity, parapharyngeal and masticator space, thyroid and parathyroid, salivary glands and lymph nodes, temporomandibular joint imaging, larynx and hypopharynx. The referencing in these chapters is reasonable. The last part of the textbook concerns paediatric neuroimaging. First there is a chapter on normal development. Chapters follow on congenital malformations of the brain and spine. Both chapters are unsatisfactory from the point of view of both contents and referencing (almost all references date from 1993 or earlier). The remaining chapters are concise and well referenced. Metabolic diseases, anoxic ischaemic injury, neurocutaneous syndromes and trau-

ma are discussed. One chapter is dedicated to hydrocephalus and CSF flow and one chapter reviews congenital abnormalities of the face. The editor points out himself that the book is meant as a master file in the field of neuroimaging, cataloguing and including all aspects of the practice of neuroimaging. The book suffers to some degree from the drawbacks of a multi-author textbook. Most chapters are excellent but there are a few that are unsatisfactory from the point of view of content and lack of recent references. Spinal imaging is treated as the poor relation since only 100 pages are dedicated to this important part of neuroradiology practice compared with more than 400 pages on head and neck imaging. Overall the book is certainly recommended as one of the possible choices when one has to decide on buying a reference book on neuroradiology. In fact the reader gets a book on neuroimaging and head and neck imaging. The high price will be a disadvantage. P. Demaerel, Leuven