Sarcoma(2000) 4, 17± 26 ORIGINAL ARTICLE Soft tissue tumours of theretroperitoneum J.FRANS GRAADTV ANROGGEN& PANCRASC.W .HOGENDOORN Departmentof Pathology,Leiden University Medical Centre,TheNetherlands Abstract Purpose. This reviewsummarizes themore prevalent soft tissuetumours arising inthe retroperitoneum and highlights somerecent fundamental and diagnostic developments relevant to mesenchymal tumours. Discussion. Theretroperitoneum is an underestimatedsite for benignand malignant neoplastic disease, andrepresents the secondmost common site of originof primary malignantsoft tissuetumours (sarcomas) after thedeep tissues ofthelower extremity.Incontrast to thepredominance of benignsoft tissuelesions over malignantsarcomas elsewhere,retroperitoneal mesenchymallesions are far morelikely tobe malignant. The differential diagnosis is primarily withthe more common lymphoproliferative andparenchymatous epitheliallesions arising inthis area, andwith metastatic disease from knownor unknownprimary sites elsewhere.The most prevalentmesenchymal tumours at this siteare of alipomatous, myogenicor neuralnature. Theirgenerally late clinical presentation and poorly accessiblelocation provides numerousclinical challenges; optimal radiologicalimaging and a properly performed biopsy are essentialcogs in the management route. Histopathological diagnosismay becomplicated, but has beenaided by developmentsin the ® eldsof immunohistochemistryand tumour (cyto)genetics.Despite signi® cant advances inoncological management protocols, theprognosis remains generallyless favourable than for similar tumoursat more accessible sites. Key words: softtissue tumour, sarcoma, review,retroperitoneum Introduction Inadultsthe majority ofretroperitonealneoplasms arepr imarylymphoproliferative (Hodgkin’sand Theretroper itoneumreprese ntsthe lumbo-iliac non-Hodgkin’slymphoma)andparenchym atous anatomical regionbou ndedan teriorlyby the epithelialtumour s(renal,adrenal, pancreas), or peritoneum,posteriorly by the posteriorabdominal representmetastatic diseasefrom known or unknown wall, superiorlyby the 12th riband vertebra, inferi- primarysiteselsewhere. 2 Ininfancy and early child- orlyby the sacrumand iliac crest and laterally by the hood,nephroblastoma (Wilms’ tumour), neuroblas- peripheralmarg inof the quadratuslu mborum toma andgerm cell tumours are the morecommon muscles.Present within the retroperitoneumare the retroperitonealneoplasms. 3 pancreasand duodenum, kidneys and ureters, adrenal Soft tissue(mesenchymal) tumours of the retroperi- glands,aorta andits branches,inferior vena cava and toneumare less common; nevertheless 15% of all its tributaries,lymph nodes and nerve branches, all primarysarcomasarise within the retroperitoneum, embeddedin alooseframework of connectivetissue. andconsequently this representsthe secondmost Therelative paucity of vital structures,and the commonsite for the originof malignantmesen- abundanceof looseconnective tissue in this area, results chymaltumours, after the deeptissues of the lower ina generallylate clinicalpresentation of space- extremity(thigh). 1 It isthe generalexperience that, occupyinglesions. Symptoms tend to berelated to althoughbenignsoft tissuelesionsat all sites gastrointestinal,urinary or vascular compromise, when outnumbertheir malignant counterparts by aratio of largelesional size and compression/ invasionof adjacent at least 100:1, inthe retroperitoneumsarcomas are structuresseverely limits the curativetreatment options. moreprevalent than theirbenign counterparts. In Collectively,malignant tumours of the retroperito- comparisonwith soft tissuelesio nselsewh ere, neumare roughly four times more frequent than however,the rangeof commonlyencountered retro- benignlesions, in sharp contrast to neoplasticdisease peritonealmesenchymal neoplasms is more limited, occurringelsewhere in the body,where benign disease with the mostcommon lesions being of alipomatous, predominates. 1,2 smoothmuscle or neural nature (T able 1). 1,2 Correspondenceto: P.C.W.Hogendoorn,MD, PhD, Department ofPathology, LeidenUniversity Medical Centre, Building I,L1-Q, PO Box9600, 2300RC, Leiden,The Netherlands. Tel: +3171 526 6639; Fax: +3171 5248158; E-mail: p.c.w.hogendoorn@ pathology.medfac.leidenuniv.nl 1357-714Xprint/1369-1643online/00/010017-10 ½ 2000T aylor &FrancisLtd 18 J.FransGraadt VanRoggen& PancrasC.W .Hogendoorn Table 1. Softtissue neoplasmsof theretroper itoneum Malignant Benign Lipomatous: Well-differentiatedliposarcoma Myolipoma Dedifferentiatedliposarcoma Myogenic: Leiomyosarcoma Neurogenic: Malignantperipheral nervesheath tumour (Anciant)schwannoma Miscellaneous: Neuro®broma Desmoplasticsmall roundcell tumour Pleomorphicsarcoma, undifferentiated Kaposiform haemangioendothelioma In¯ammatory myo® broblastic tumour Whilemost of the betterdifferentiated retroperito- It isthe aimof this shortsynopsis to discussthe neallesion sgenerally donot posesign i®can t mostprevalent retroperitoneal soft tissuetumours diagnosticproble ms,high -gradesarcom as may andassociated differential diagnoses, and to highlight presentmor phologically as poorlydifferent iated someimportant recent developments in fundamental tumourslackingdistinct ive phenotypicfeatures. anddiagnostic aspects of mesenchymaltumours. Consequently,histomorpholo gicaland ultrastruc- turalanalysis may beinsufficient for reaching an Thehistopathology of retroperitonealsoft tissue accurate(differentia l) diagnosisin cer tain cases, tumours essentialfor directing patient managementstrategies. Fortunately,it has becomeapparent overthe last Thesoft tissuesare de® ned as consistingprimarily of decadethat certainsoft tissuetumours appear to be extraparenchymatousvoluntary muscle, fat, ®brous associatedwith tumour-speci®c geneticalterations (connective)tissue, and the neurovascularsupply of (Table 2), and(cyto)genetic analysis aimed at the thesetissues. 1 Nevertheless,mesenchymal tumours detectionof thesealterations is a helpfuladjunct in alsoregularly arise from the supportingconnective resolvingsome of thesediagnostic dilemmas. 4 tissuesof the variousorgans and are included in this Computerizedtomography(CT) scanningand review. (dynamic)magnetic resonance imaging (MRI) are the radiologicalprocedures of choicein determining Reactive non-neoplastic processes the extentof local,regional and distant tumour spread.These procedures are essential for clinical Retroperitonealmasses may beof anon-neoplastic staging,planning an appropriate and optimal biopsy orneoplastic nature. Non-neoplastic masses arising procedureprior to de®nitive treatment, as wellas at this siteare pred ominantly of areactive/ playingan important role in follow-up imaging to in¯ammatory orinfectious nature, involving either assessefficacy of treatmentregimens. 5± 7 Addition- the organsat this siteor the retroperitonealsoft tissues. ally, positronemission tomography (PET) scanning Thesegenerally do not pose a clinicalproblem, may, incertainsettings, be of clinicaluse, particularly althoughperiodically the differentialdiagnosis with inthe detectionof high-gradesarcomas and the neoplasticdisease may bemore complicated; for assessmentof localrecurrence. 8,9 examplethe differentialdiagnosis of reactive® brosis Table 2. Genetic alterationsof diagnostic signi® cancein thesarcoma group Tumour Geneticalteration Gene(s) Alveolar rhabdomyosarcoma t(2;13)(q35; q14) FKHR/PAX3 t(1;13)(q36; q14) FKHR/PAX7 Atypical lipoma/well-differentiatedliposarcoma ring(chr. 12)/ marker chromosome ? Desmoplasticsmall roundcell tumour t(11;22)(p13; q12) EWS/WT1 Ewing’s sarcoma/PNET t(11;22)(q24; q12) EWS/FLI1 t(21;22)(q22; q12) EWS/ERG t(7;22)(p22; q12) EWS/ETV1 Gastrointestinalstromal tumour mutationchromosome 4q11-21 c-kit losses chromosome14q Myxoidliposarcoma t(12;16)(q13; p11) CHOP/FUS t(12;22)(q13; q11) CHOP/EWS Synovial sarcoma t(X;18)(p11.2; q11.2) SYT/SSX1 SYT/SSX2 Soft tissue tumours ofthe retroperitoneum 19 (sometimesseen with non-Hodgkin’slymphoma) 10/ Liposarcoma ÐLiposarcomasare the mostcommon idiopathicretroperitoneal ® brosis(an in¯ammator y/ soft tissuetumours occurring within the retroperito- reactive processoften presenting as amass) 11,12/ neum,and probably accountfor 25± 35% of all mesen- retroperitoneal® bromatosis, 12 at this siteregularly chymal lesionsat this site. 21± 23 Althoughthe seenin the context of Gardner’ssyndrome 13/ liposarcomag roupis subdiv idedinto well - ®brosarcoma(rare), 12 andthe differentialdiagnosis differentiatedliposarcoma, dedifferentiated liposar- of xanthogranulomatouspyelonephritis coma,myxo id/roundcell liposa rcoma,an d (in¯am matory) 14/(sarcomatoid)renalc ell pleomorphicliposarcoma, the majority of retroperi- carcinoma15/soft tissuesarcoma with axanthogranu- tonealliposarcomas are of the well-differentiatedand lomatousmorphology . 12 dedifferentiatedtype. 22 Myxoid/roundcell liposar- comaoccur far lessfrequently in the retroperito- Neoplastic disease neum,while pleomorphic liposarcoma at this siteis very rare.22 Well-differentiatedand dedifferentiated Asalluded to earlier,the majority of retroperitoneal liposarcomashould probably beregarded as related tumoursare primary lymphoproliferative and paren- entitiessince the latter oftenarises from/ withinthe chymatousepithelial tumours. former,23± 25 andcommon genetic alterations are Themajority of lymphomasare non-Hodgkin’ s presentin these tumours (ring chromosomes derived B-celltype, butthese may beassociated with avari- fromchromosome 12 andlarge marker chromosomes; able degreeof contiguous® brosis/sclerosissometimes Table 2).26,27 Similarly(cyto)genetic