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  Volume 94
Numero 4
July - August 2008 		I documenti sono in formato PDF, consultabili utilizzando Acrobat Reader
 
Congenital tumors of the retrorectal space in the adult: report of two cases and review of the literature
Claudio Coco, Alberto Manno, Claudio Mattana, Alessandro Verbo, Daniel Sermoneta, Gianluca Franceschini, Annamaria De Gaetano, Luigi Maria Larocca, Luigi Petito, Giorgio Pedretti, Gianluca Rizzo, Claudio Lodoli, Domenico D’Ugo
1Department of Surgery, 2Department of Radiology, and 3Department of Pathology,
Università Cattolica del Sacro Cuore, Rome, Italy

Key words: retrorectal tumors, teratoma, dermoid cyst.

abstract
Aims and background. To describe and discuss, on the basis of the authors’ experience and a review of the literature, the main aspects regarding the etiology, diagnosis, treatment and prognosis of congenital tumors of the retrorectal space.
Methods. We present 2 cases of congenital retrorectal tumors, a sacrococcygeal teratoma and a dermoid cyst, which represent, from the pathogenetic point of view, the most frequent presentation of the rare tumors of the retrorectal space.
Results. The reported cases are typical. The teratoma presented as an encapsulated, mixed mass located in the pelvic cavity behind the rectum and the vaginal canal, without signs of sacral involvement. The dermoid cyst appeared as a unilocular lesion filled with sebum and hair, which extended laterally to the iliopubic branch, medially to the urethra and anal canal, and posteriorly to the adipose tissue of the right buttock. Pelvic MRI produced a precise picture of the extension of the lesion and of the relationship between the mass and the pelvic organs and surrounding bony structures. Both lesions were completely removed via the perineal approach without coccygectomy. No recurrences were observed at 2 years of follow-up.
Conclusions. Congenital retrorectal tumors are rare. MRI is crucial for diagnosis and preoperative planning. Complete surgical removal is the treatment of choice. Resection of the coccyx is necessary only in case of its involvement by the neoplastic mass or suspected malignant transformation.

Introduction
Although congenital retrorectal tumors are extremely rare in the adult, they must be taken into account whenever a patient presents with a posterior palpable mass at rectal examination, especially if associated with gluteal involvement. The diagnostic workup and surgical approach are extremely challenging and the prognosis of malignant lesions is often poor. With the 2 cases presented here we try to contribute to the understanding of the main issues related to these lesions, with special attention to the problems regarding surgical treatment.
Case reports
Case 1
A 40-year-old woman with a history of a pelvic mass since birth was admitted to our department for gradually increasing pelvic pain. The patient’s past medical history was significant for nephrolithiasis treated by ureterolithotomy. Blood test results were within normal ranges.
Physical examination showed a painful palpable mass in the right buttock; gynecological and rectal examinations were negative for intraluminal modifications and confirmed the presence of a large palpable mass in the right pelvis.
Axial T1- and T2-weighted MRI scans showed an oval multiloculated mass with several septa and a variable signal during the different sequences consistent with serous fluid content, fluid-fluid level, and mucinous content (Figure 1). The mass was located in the pelvic cavity behind the rectum and the vaginal canal, which seemed to be anteriorly displaced, without signs of sacral involvement.
Sagittal T1- and T2-weighted images showed a cyst in the presacral space with a heterogeneous content and a variable signal. It appeared in close relation to the anterior surface of the coccyx, compressing and anteriorly displacing the uterus but without any signs of bone involvement (Figure 2).






Carcinoembryonic antigen, CA 15-3, CA 19-9, AFP and beta-HCG levels were in the normal range, while CA 125 was increased (109 ng/mL). The mass was completely excised by a perineal approach. Through a longitudinal incision centered on the lesion, the subcutaneous planes were divided and the lumbosacral fascia was exposed. The coccyx was mobilized by transection of the anococcygeal ligament. The retrorectal space was exposed by transection of the fibers of the levator ani. The mass was carefully dissected and isolated, with special attention to avoiding rectal perforation. The pelvic floor was then reconstructed by simple suture of the fibers of the levator ani, with no need for a prosthetic mesh.



Macroscopically, the tumor consisted of a globular mass with a white external surface and a diameter of 18 cm (Figure 3). The cut surface was cystic and solid, with the cysts being filled with keratinous and serous fluid and the solid areas with fibrous, adipose and cartilaginous tissue (Figure 4). The tumor was composed of adult-type tissues representing all 3 germ layers. The endodermal derivative included respiratory epithelium; the mesodermal derivatives included cartilage and fat; the ectodermal derivatives predominated in the cyst lining, which was composed of epidermis and underlying skin appendages.






The tissues were often arranged in an organoid fashion with cartilage and mucinous gland beneath respiratory epithelium. Focal cyst rupture resulted in a foreign-body reaction to keratin (Figure 5A and 5B).
The postoperative course was uneventful. Follow-up MRI at 1 and 2 years showed no local relapse.
Case 2
A 50-year-old man was referred to our department for a 25-year history of a pelvic mass that was gradually increasing in volume. The patient’s past medical history was unremarkable. Blood tests were all normal and no increase in CEA, CA 15-3, CA 19-9, AFP, beta-HCG or CA 125 was registered.
Physical examination showed a large palpable mass in the right buttock. Rectal examination showed no intraluminal masses.
Axial MRI scans revealed an oval mass with a hyperintense signal on T2- weighted images indicating fluid content. The mass had a regularly margined thin wall and there was no evidence of internal septa (Figure 6). It extended laterally to the iliopubic branch and medially to the urethra and anal canal, which were displaced contralaterally, and developed posteriorly up to the adipose tissue of the right buttock.






The coronal T2-weighted image showed a hyperintense oval mass filling the right ischiorectal fossa (Figure 7). The tumor was in close relation to the levator ani rostrally, the internal obturator muscle laterally, and the rectum medially. No signs of sacral invasion were identified.
Also in this case we chose a perineal approach, which allowed complete resection of the mass (see case 1 for technical details). The gross findings corresponded to a cyst with a diameter of 8 cm, filled with yellow sebaceous material and hair.
The cyst lining was composed of epidermis and underlying skin appendages. Mitotic figures were absent. The external surface of the cyst was surrounded by inflammatory cells including histiocytes and foreign–body-type giant cells. Also in this case was the postoperative course uneventful; follow-up MRI scans at 1 and 2 years and serum marker measurements were negative.
Discussion
The retrorectal or presacral space is defined anteriorly by the fascia propria of the rectum, and posteriorly by the presacral fascia. It is laterally bordered by the lateral stalks of the rectum, the ureters and the iliac vessels, and extends superiorly to the peritoneal reflection of the rectum and inferiorly to Waldeyer’s fascia1. It is an area of development of multiple embryonic structures, from which a heterogeneous group of both benign and malignant tumors may develop1. Tumors of the retrorectal space are rare. The most representative series from the United States report an incidence varying from 1.4 to 6.5 cases per year2-6. According to their pathogenesis, retrorectal tumors are classified into 5 categories: congenital, inflammatory, neurogenic, osseous and miscellaneous1. The 2 cases described in the present report, a sacrococcygeal teraroma and a dermoid cyst, are examples of the most common type of retrorectal tumors, the congenital type, which accounts for 55% to 70% of all retrorectal masses5-7. Teratomas are defined as tumors containing tissue foreign to the anatomical site where they originate which derives from at least 2 germ cell layers8, while dermoid cysts are unilocular lesions lined by squamous mature epithelium and filled with sebaceous material and glands9. Caudal embryonic vestiges are thought to give rise to dermoid cysts, while teratomas probably derive from a primordial germ cell deviated from its migratory pathway from the yolk sac to the gonads8. In the case of the sacrococcygeal location, this aberrant migratory pathway ends in Hensen’s node (primitive knot), where the totipotential cells, once migrated caudally up to the coccyx, can grow down into the gluteal area or up into the abdominopelvic cavity10,11. On the basis of their prevalent way of diffusion, teratomas can be divided into 4 categories10 (Table 1). The case illustrated in the present report can be classified as type II.

Table 1 - Classification of sacrococcygeal teratomas according to location11

Type

External

Intrapelvic

 

component

component

 

 

 

I

Yes

No

II

Yes

Yes (dumbbell shaped)

III

Yes

Yes*

IV

No

Yes°

 

 

 

*Predominant.

°Intrapelvic or presacral.


From a macroscopic point of view, the reported cases were typical: the teratoma presented as an encapsulated mass of 18 cm in largest diameter (the median reported size is 8 cm8) with the cut surface appearing as a mixture of solid and cystic areas, while the dermoid cyst was a thin-walled, unilocular tumor of 8 cm in largest diameter filled with yellow sebaceous material and hair. As confirmed in the present report, no malignant degeneration has ever been described in retrorectal dermoid cysts, while the degree of differentiation of teratomas can vary from benign (as in the present case), when the mass is composed of mature and well differentiated tissues, to immature but without malignant features, up to frankly malignant, containing germ-cell elements 12. Even if a tendency toward malignant transformation with increasing age has been described among the pediatric population, case reports describing benign lesions predominate in adult patients4,13.
The symptoms of congenital retrorectal masses are often subtle and nonspecific and, if present, result directly from compression of surrounding structures by the mass causing pain, constipation, narrowed stools or pollakiuria14. A particular, life-threatening condition is vaginal canal obstruction, which may lead to dystocia during childbirth. This underlines the necessity of surgical resection of any retrorectal mass in fertile women, even if benign and asymptomatic1. In case of malignant invasion by the tumor, neurological symptoms such as lower extremity paresthesias or weakness may occur5. Nevertheless, most of these masses are asymptomatic and discovered on routine screening rectal examination but, because they are often soft and compressible, they are easily missed if the examiner does not maintain a high index of suspicion during the procedure1.
Although conventional plain films can demonstrate structural abnormalities of the coccyx and sacrum, including bone destruction in case of malignancy8 and the presence of calcifications in mature teratomas1, pelvic CT and especially MRI are the most important diagnostic tools when dealing with a retrorectal tumor. Both techniques show high sensitivity and specificity in the identification and morphological characterization of these masses, allowing to distinguish between solid, cystic and mixed lesions, identify the presence of fat or calcifications8, establish the extension of the mass and its relationship to pelvic structures2,5,8 and, finally, assess possible bone invasion or nerve involvement2,5. On the basis of such considerations, we decided to submit both of our patients to pelvic MRI, which gave us a precise picture of the mass’s extension, with particular reference to its location in the pelvic cavity and the amount of external component. Extremely precise was also the identification of the relationship between the mass and the pelvic organs, the pelvic floor muscles, and the surrounding bony structures. All of this information proved crucial for our preoperative planning.
When a retrorectal mass has been identified, the differential diagnosis is often extremely challenging and requires the convergence of clinical and radiological data from CT and MRI. In the first case described here, the complex morphological picture of the lesion made it necessary to distinguish it from other congenital retrorectal tumors such as multilocular tailgut cyst, inflammatory masses like chronic retrorectal abscesses, or neurogenic or bone tumors such as neurofibroma, fibrosarcoma, ependymoma and ganglioneuroma. The second case described in this report presented as a simple unilocular cystic lesion and the differential diagnosis involved mainly the exclusion of a meningocele or a rectal duplication. Neither of the lesions showed destructive or invasive features, as in the case of frankly malignant tumors like chordomas, or metastatic deposits 15. In such cases there is almost unanimous consent to avoid a needle biopsy for diagnostic confirmation, as many studies suggest that this procedure may result in tumor seeding3,5 or infect previously sterile cystic lesions1.
The cornerstone of the treatment of congenital retrorectal masses is complete surgical excision, which should be combined with systemic chemotherapy and/or radiotherapy in patients with malignant lesions1,8. Three factors are crucial when planning surgery: the approach, the advisability of extending the resection to the coccyx or sacrum, and the often difficult dissection of the mass from the rectum. The approach can be abdominal, perineal or combined1. The abdominal approach is to be reserved for lesions whose lowest extent is above the level of the fourth sacral element because it allows the best exposure of the pelvic structures2. The perineal approach was chosen in both cases described in the present report. We obtained optimal exposure of both the tumor and the retrorectal space through a longitudinal incision centered on the lesion, although a transverse incision overlying the coccyx is more commonly adopted1. Despite the intrapelvic extension and the size of the mass, which, in the first case, was larger than what is generally considered suitable for the perineal approach alone15,16, in our experience it allowed easy mobilization of the intrapelvic component of the tumor without the necessity of abdominal access. We think that the combined approach is to be reserved for very large tumors extending both proximally and distally to the fourth sacral element or to frankly malignant lesions with an infiltrative pattern that makes isolation of the mass impossible by the perineal approach alone. These cases are often extremely challenging, especially when a partial sacrectomy is necessary. Total sacrectomy is, fortunately, rarely needed and has been performed only for lesions involving S-1 17. Whatever the size of the mass, resection of the coccyx is commonly advocated as crucial in order to obtain complete surgical removal of the mass3,12,18. This indication is based on the observation that the coccyx can harbor neoplastic cells, and the risk of recurrence is extremely high if it is not completely removed12,19. Nevertheless, we followed the more recent attitude of performing resection of the coccyx only when it is invaded by the tumor or in cases of frank malignancy or highly suspected malignant potential1. We believe this attitude was correct in our patients because neither had relapsed at 2-year follow-up. Particular attention was paid to the isolation of the tumor from the rectum because, as is commonly seen, it was closely adherent to the mass, and gross dissection could easily result in a postoperative fistula, a complication reported in about 3% of cases3,19. After complete surgical removal the prognosis is good only in histologically benign cases13,19, while malignant lesions have a high tendency to relapse locally or at distant sites, and the prognosis is extremely poor, also when the patient is treated with adjuvant chemotherapy and/or radiotherapy17.

References
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 3. Cody HS 3rd, Marcove RC, Quan SH: Malignant retrorectal tumors: 28 years’ experience at Memorial Sloan-Kettering Cancer Center. Dis Colon Rectum, 24: 501-506, 1981.
 4. Freier DT, Stanley JC, Thompson NW: Retrorectal tumours in adults. Surg Gynecol Obstet, 132: 681-686, 1971.
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 8. Keslar PJ, Buck JL, Suarez ES: Germ cell tumors of the sacrococcygeal region: radiologic-pathologic correlation. Radiographics, 14: 607-620, 1994.
 9. Dahan H, Arrivè L, Wendum D, Le Pointe Docou H, Diobri H, Tubiana JM: Retrorectal developmental cysts in adults: clinical and radiologic-histopathologic review, differential diagnosis and treatment. Radiographics, 21: 575-584, 2001.
10. Altman RP, Randolph JG, Lilly JR: Sacrococcygeal teratoma: American Academy of Pediatrics Surgical Section Survey. J Pediatr Surg, 9: 389-398, 1974.
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14. Killen DA, Jackson LM: Sacrococcygeal teratoma in the adult. Arch Surg, 88: 425-433, 1964.
15. Audet IM, Goldhahn RT Jr, Dent TL: Adult sacrococcygeal teratomas. Am Surg, 66: 61-65, 2000.
16. Abel ME, Nelson R, Prasad ML, Pearl RK, Orsay CP, Abcarian H: Parasacrococcygeal approach for the resection of retrorectal developmental cysts. Dis Colon Rectum, 28: 855-858, 1985.
17. Tomita K, Tsuchiya H: Total sacrectomy and reconstruction for huge sacral tumors. Spine, 15: 1223-1227, 1990.
18. Ng EW, Porcu P, Loehrer PJ: Sacrococcygeal teratoma in adults. Case report and a review of the literature. Cancer, 86: 1198-1202, 1999
19. Miles RM, Stewart GS: Sacrococcygeal teratomas in adults. Ann Surg, 179: 676-683, 1974.


 
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