Presacral lesions usually occur between the age of 40 and 60. They are classified by their predominant cell line

type. Five categories are obtained: congenital, inflammatory, neurogenic, osseous and miscellaneous (Table 4) [4] [10] [19] . Lev-Chelouche et al. suggest another classification based on tumor origin and nature, but this has no influence on the management of an individual patient [14] .

All lesions in this study were congenital. This category accounts for 55% to 70% of all presacral lesions. Developmental cysts include epidermoid cysts, dermoid cysts, tailgut cysts or teratomas, accounting for 60% of all congenital lesions [4] [8] [9] [20] . They have a male:female ratio ranging from 1:2 to 1:5, partly explained by findings during routine gynecologic investigations [2] [4] [7] . This concurs with our findings: female predominance (83.3%) was noted in developmental cysts and one patient was referred by a gynecologist. The most common malignant presacral lesion is a chordoma. It has a male:female ratio of 2:1. Chordomas are usually slow growing lesions, rarely occur before the age of 30 and frequently cause pain and nerve impingement [4] [8] [10] . We encountered one chordoma in a 40-year-old male. He was asymptomatic, apart from sacral swelling due to tumor extension behind the sacrum. Inflammatory lesions represent abscesses, fistulas and granulomas. Some series do not include those lesions [10] . Neurogenic lesions arise from peripheral nerves, representing 10% of all presacral lesions. Ependymomas have the highest incidence in this category. Osseous lesions represent 5% to 10% of all presacral masses. Miscellaneous lesions are very diverse, accounting for the remaining 10% to 25%. Metastatic disease, usually from the rectum, constitutes an important part [4] [8] [10] .

The asymptomatic or nonspecific presentation delays the correct diagnosis of presacral lesions. Series report 14% to 56% of cases without symptoms [1] [2] [9] [14] -[16] [18] [20] . We reported 85.7% of patients having at least one symptom on detailed questioning. Misdiagnoses include fistula in ano, perianal abscesses, proctalgia fugax, pilonidal disease, psychogenic pain, back pain and postpartum pain [7] [21] . Singer et al. report seven cases which had undergone an average of 4.7 invasive procedures before being correctly diagnosed with a presacral lesion [7] . Other results conclude that 36.2% of the cases had undergone a previous procedure [16] . If symptomatic, duration between symptoms and diagnosis is an average of twelve months [1] . Possible symptoms are caused by compression, invasion, infection, necrosis or malignancy [8] -[10] [14] . Pain complaints of the perineum, back and abdomen are the most common symptoms [1] [4] [15] [16] [18] [20] [22] -[24] . Glasgow et al. conclude that male gender, an age over 60 years and pain is suggestive of malignancy. Pain complaints occur

in 86% to 88% of malignant lesions, in contrast to 22% to 39% of benign lesions [1] [2] . Our findings do not concur with this conclusion: pain or dyspareunia was reported in five benign lesions (83.3%), while none were noted in the chordoma. Other common symptoms include constipation, overflow diarrhea and tenesmus, which we reported in three cases [8] [16] [18] [22] [24] . Many other, but less common symptoms are described. None were seen in this study. Sexual dysfunction, pain of lower limbs and dysfunction of lower limbs are caused by invasion of the sacral plexus. A recurrent fistula, an abscess or a secreting sinus could be a sign of an infected presacral mass [4] [7] [9] [10] [17] . Life-threatening dystocia, due to obstruction by a presacral mass, has been described in several case reports [25] [26] . A meningocele can cause postural headache and acute meningitis [27] . Anorectal stenosis is suggestive of a Currarino triad, consisting of an anorectal malformation, a sacral bony defect and a presacral mass [28] .

The sensitivity of digital rectal examination is inconsistent. Several series report 75% to 100% of the presacral lesions to be palpable [1] [4] [14] [16] [17] [23] . Glasgow et al. and Bosca et al. report respectively only 35% and 47.6% to be palpable [2] . Differences are attributed to the location and the extent of selected tumors. Lesions below S3 can be palpated on rectal examination [7] [15] [21] . This concurs with our findings. If the lesion is present on rectal examination, estimation of tumor size, location, mobility, consistency and lobulation is possible [10] [29] [30] .

We conclude that clinical awareness is important to detect presacral lesions, because they are usually slow growing and latent in onset. Knowledge of possible symptoms is necessary. A digital rectal examination is recommended, as it can detect lesions below S3. Further investigations are always indicated.

Diagnosis of presacral lesions is based on imaging and histology: MRI has become the cornerstone in the preoperative work-up and pathological examination confirms the classification [3] [5] [10] [18] .

Due to the excellent soft-tissue resolution and multiplanar capacity, MRI is the best imaging modality to assess tumor location, size, morphology and adjacent structures [5] [6] [10] . The risk of malignancy can be estimated based on following features: heterogeneity, solid appearance, irregular or infiltrative borders, variable enhancement after gadolinium administration, rapid growth and extension above S3 [3] [5] [18] . Our findings predicted malignancy with 100% accuracy, confirming the current literature. Biological behavior also correlates with diffusion restriction. DWI can distinguish benign and malignant lesions, using quantitative ADC measurements. Several authors report significantly higher ADC values at high diffusion gradients for benign lesions [31] -[33] . Our findings concur with this conclusion. Specific diagnosis by MRI is difficult. Glasgow et al. report 28% of MRI diagnoses to be in accordance with the histological diagnosis [2] . Radiological evaluation provided a differential diagnosis in order of preference. Accuracy was 57.1%: two epidermoid cysts were mistaken for tailgut cysts and one tailgut cyst was mistaken for endometriosis. Presacral cysts usually have low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. This may be influenced by the cyst’s content: blood, proteins and mucins cause higher signal intensity on T1-weighted images. Fat content is best seen on T1-weighted images using fat suppression. This is suggestive of a dermoid cyst. Tailgut cysts are multicystic, in contrast to other cystic masses. A chordoma is lobulated with a heterogeneous high signal intensity on T2-weighted images and low-intermediate signal intensity on T1-weighted images. Gadolinium injection reveals a heterogeneous enhancement with a honeycomb appearance [5] [18] [34] .

CT allows us to detect presacral lesions, differentiate cystic from solid lesions and evaluate tumor extent [1] [4] [9] . The soft-tissue resolution remains inferior to MRI. Glasgow et al. report 18% of radiological diagnosis to be in accordance with histology [2] . Multi-slice CT illustrates an evolution in reconstructing and evaluating section planes [35] . CT findings always indicated the need for additional MRI to precisely define tumor characteristics.

Other technical investigations are of lesser value. Plain X-rays can reveal a mass, sacral destruction or calcifications. Calcifications are suggestive of a teratoma [4] [21] . A scimitar sign is typical for an anterior meningocele [10] [27] . X-rays are neither sensitive, nor specific and downplay possible damage [34] . Developmental cysts can be misdiagnosed as a chronic draining sinus. Fistulography can identity a presacral lesion as their origin [10] . Endoscopy can reveal an extra-luminal compression in large lesions. An edematous rectum wall is suggestive of an infected cyst [21] . Sensitivity of endoscopy has been documented at 53 percent [2] . TRUS is an inexpensive method to roughly estimate the extent of presacral lesions and their relation to the adjacent structures [6] [36] . One patient underwent TRUS to evaluate his prostate, but no presacral lesion was documented.

The role of biopsy is limited. Complications include fistula formation, abscess formation, tumor seeding, recurrence or meningitis [2] [18] [22] [30] . Transrectal biopsy is never recommended. CT-guided extrarectal or presacral biopsy is considered in inoperable cases if it changes the non-operative treatment (for example metastatic disease and lymphomas) [10] [37] [38] .

Histological conformation is made postoperative and determines further follow-up. Epidermoid cysts are unilocular lesions, which are lined with stratified squamous epithelium and filled with clear fluid. They do not contain skin appendages, in contrast to dermoid cysts [8] [34] . Tailgut cysts are multicystic lesions, filled with mucoid contents and lined with ciliated columnar cells, squamous cells and transitional cells [20] [34] . Rectal duplication cysts are differentiated based on following criteria: an organized smooth-muscle coat (desmine staining), continuity with the rectum and a mucosal lining similar to the rectal mucosa [34] . Teratomas are diagnosed based on their three germ layers [9] [34] . The microscopic hallmark of chordomas are the physaliphorous cells, which contain glycogen or mucin. Conventional chordomas are characterized by the absence of mesenchymal components, in contrast to chondroidchordomas and chondrosarcomas. S-100 protein expression is typically present in both chordomas and chondrosacromas, while the latter does not express cytokeratin [39] .

We conclude that MRI is the best way to evaluate the extent and characteristics of a presacral lesion. The aim is to choose the appropriate surgical approach and estimate the extent of the operation. Specific histological diagnosis is determined postoperative.

Surgical resection is required. Presacral lesions can grow and cause obstruction or invasion. Benign lesions risk causing bleeding, dystocia, infection (for example cysts or meningoceles) or malignant transformation (for example teratomas). Malignant lesions must be excised to prevent metastasis and improve life expectancy [1] -[4] [14] [16] [21] .

Resection is possible through an anterior (abdominal), posterior or combined (abdominosacral) approach. This is determined by two steps:

1) Tumor extent: above or below S3.

2) Involvement of the sacrum, the pelvic sidewall and the viscera.

Woodfield et al. propose an algorithm for the surgical management of presacral tumors. A posterior approach is used for tumors below S3. Sacrectomy is necessary in case of difficult access, large tumors or sacral involvement. Tumors above S3 or tumors with involvement of the pelvic sidewall or the viscera require an anterior approach. A combined approach is recommended in the following cases: tumor extension above and below S3, sacral invasion in lesions above S3 and involvement of the sacrum with the pelvic sidewall or the viscera in lesions below S3 [3] . Other series report similar conclusions, but the proximal border differs between S2, S3 and S4 [2] [4] [10] [18] [23] [24] [30] .

Several posterior approaches are described: perineal, transsacral, transanal, intersphincteric, transsphincteric and transvaginal. Table 5 provides an overview of their uses and limitations [3] [6] [9] [10] [17] [20] [40] -[42] .

The transsacral approach represents a minimally invasive way to provide an excellent view of low-lying presacral tumors and sacral nerve roots. Kraske’s approach lost support because of high rates of morbidity (70%) and recurrence (90%) of distal rectal cancer [43] . Local posterior excision of early rectal cancer still has a place in selected patients, but a transanal approach is preferred [44] [45] . Kraske’s approach is successfully used for presacral lesions resulting in low morbidity, recurrence and mortality [3] [16] [21] [40] . Complications include

intraoperative bleeding, fistula development, wound infection, rectal injury, incontinency, impotency and recurrence [1] [2] [15] [18] [23] [24] [40] . Blood loss is minimal with little need for transfusion [2] [16] . There was no transfusion required in our series. Intraoperative bleeding can be dangerous, as this approach does not allow for good visualization of the vasculature [6] [15] [23] . Pelvic packing may be necessary to stop the hemorrhage [15] [18] . Partial sacrectomy and intraoperative cystic drainage allow for better oversight, although cystic drainage increases the risk of seeding [15] . An extraperitoneal iliac incision for vascular isolation can be useful in large tumors [6] . Fistula formation is a common complication [40] [43] [46] . Recent series report less fistula formation (0% - 20%) if Kraske’s approach is strictly used for presacral instead of rectal lesions [1] [3] [16] -[18] [22] [24] . Rectal damage increases the risk of postoperative fistulas. We reported no fistulas, although partial excision of the rectal wall was needed in six cases. Inserting a finger in the rectum helped to differentiate rectal fibers from surrounding tissues and also prevented rectal injury. Preoperative bowel preparation is indispensable. Recent studies report an incidence of wound infections between 4.3% and 30% [1] [14] -[16] [18] [22] [24] . This is consistent with our findings (28.5%). Postoperative antibiotic prophylaxis remains important. One infection occurred after resecting a large mass (>10 cm). Flap transfer can provide a solution by preventing traction and improve healing in large defects. It is also useful in preventing wound dehiscence after partial sacrectomy [2] . We encountered involuntary contractions of the gluteus muscle after a gluteus flap transfer. There were two possible explanations: resection of the sacrum caused partial removal of the anchoring of the gluteus musculature or placement of a transgluteal drain damaged a motoric nerve. The contractions improved with physiotherapy. In our series, resections were limited to the level of S4. Incontinence and impotency are complications due to nerve damage: a unilateral S3 root must be preserved [2] [9] [10] .

Prognosis depends on the pathology and surgical margins [4] [10] . Benign lesions are more likely to be resected completely compared to malignant lesions [14] [15] . Little manipulation and no laceration of the tumor are important factors in preventing recurrence [14] . Partial sacrectomy is associated with less recurrence compared to a perineal approach, especially for cystic lesions and teratomas [9] [20] . En bloc resection is important when surrounding structures are involved [3] . Lev-Chelouche et al. report different recurrence and survival rates for benign, malignant, congenital and acquired lesions [14] . We report no significant morbidity, recurrence or mortality, bearing in mind the large proportion of benign lesions (85.7%). Benign lesions have a survival rate of approximately 100% with a low recurrence rate [4] [10] [17] . Jao et al. report 15.2% recurrence of benign lesions [1] . Malignant lesions have a worse prognosis. Jao et al. report an overall five-year survival rate of 17%, although chordomas have a better prognosis (five-year survival rate of 75%) [1] . Glasgow et al. report a 100% recurrence rate with a median disease-free time span of 24 months [2] . Woodfield et al. report recurrence in two of seven malignant lesions, both chordomas [3] . Reports of a longer recurrence-free interval after aggressive postoperative radiation therapy remain anecdotal [2] . We report no recurrence or mortality ten years after radical resection of a chordoma.