Introduction

Retrorectal tumors are rare and heterogeneous, with an estimated incidence of one in every 40,000 hospital admissions [1,2,3].

The retrorectal space is confined by the rectum with its mesorectal fascia anteriorly, the parietal pelvic fascia posteriorly and the peritoneum cranially. The distal end of the retrorectal space is defined by the fusion of the presacral, parietal pelvic fascia and mesorectal fascia, which cover the levator ani muscle. The parietal fascia separates the retrorectal space from the presacral space. The iliac vessels and ureters are located laterally [2, 4, 5].

The histologic diversity of retrorectal tumors with benign or malignant lesions results from the embryologic development, during which endo-, meso-, and ectodermal tissues undergo modifications. Tumors can be related to any of these. Retrorectal tumors are commonly categorized as congenital, neurogenic, osseous, inflammatory and miscellaneous [6,7,8].

Most tumors remain asymptomatic or present with nonspecific symptoms and are often diagnosed incidentally [3]. Occasionally, they present as a palpable mass on digital rectal examination. Clinical examination, computed tomography (CT) and magnetic resonance imaging (MRI) are considered the gold standard for preoperative evaluation [1, 9,10,11]. Determining the exact anatomical location is essential to the surgical approach. A biopsy can be considered, although its value remains controversial [8, 12]. Retrorectal tumors should be completely resected, even if they are asymptomatic.

Due to their rarity and diverse clinical presentations, diagnosing and treating retrorectal tumors remain challenging. We share our 20-year experience with 21 patients, comparing it with existing literature.

Patients and methods

In our retrospective study, we identified 21 patients treated for retrorectal tumor at the Surgical Department of the University hospital Erlangen between 2002 and 2022. Of these, 20 underwent surgery. We analyzed demographic characteristics (i.e., age, gender), symptoms, diagnosis, treatment (i.e., surgical approach, resection of bone structure), postoperative complications (Clavien-Dindo classification [13]), histopathology and local recurrence. Data were obtained retrospectively from the patient record.

Furthermore, in a literature review (Fig. 1), we performed a Pubmed search on January 6, 2023 for abstracts from 2002 to 2023 with the terms “retrorectal tumors” (n = 360) and “presacral tumors” (n = 1058). Publications with fewer than 20 cases were excluded, as were reviews, manuscripts not available in english, pediatric cases and duplications in both search terms. The remaining publications (n = 39) were scrutinized and data extracted to tabulate the findings according to publication year, number of patients, gender, age, histopathology, rate of malignancy, surgical approach, postoperative morbidity, follow-up and local recurrence.

Fig. 1
figure 1

Overview of literature search

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Results

Patient characteristics are presented in Table 1. Thirteen were female (62%) and eight male (38%). The median age at operation (or, in the non-operated patient at first diagnosis) was 54 years (range 19–74 years). Thirteen patients (62%) presented with nonspecific symptoms: pain in the back, flank, pelvis, lower abdomen, anus or a feeling of anal pressure. One patient had right-sided weakened foot dorsiflexion. Eight patients (38%) were diagnosed incidentally during gynecologic examination, treatment of anal fistula, on MRI or CT for other reasons, and during a gynecologic operation.

Table 1 Characteristics and diagnostics of the 21 patients with retrorectal tumor
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MRI was performed in 20 (95%) patients (Fig. 2), CT scan in 9 (43%), endosonography in 7 (33%) and rectoscopy or colonoscopy in 17 (81%). Biopsies were obtained in 10 (48%).

Fig. 2
figure 2

58-year-old patient with a retrorectal schwannoma on preoperative MRI:  sagittal T2 (A),  axial T2 (B), and the postoperative macroscopic view of the schwannoma (C)

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Treatment

Twenty patients underwent surgery (Table 2); one patient with choroidal melanoma metastasis (diagnosis confirmed by biopsy) underwent radio- and immunotherapy.

Table 2 Surgical treatment and outcome of the 21 patients with retrorectal tumor
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A posterior approach (Kraske procedure) was used in 14 patients (70%) and an anterior approach in five (25%). A combined approach was required in one patient (5%). Resection of bone structures was necessary in nine (45%).

Postoperative complications occurred in seven patients (35%): three with wound healing disturbances and one each with a voiding dysfunction, a wound seroma, a hematoma and constipation. All seven patients reported pain. According to the Clavien-Dindo classification, category I occurred in four patients (20%), II in one (5%) and III in two (10%). Four patients had a local recurrence during a median follow-up of 10 months (range 1-166 months) and a mean follow up of 42 months. Reoperation was not required. There was no mortality observed.

Histopathologic findings

Histopathologic findings varied widely (Table 3). Seventeen patients (81%) had a benign lesion, the most common being a tailgut cyst in 10. In one patient it remained unclear whether the lesion was a tailgut or a duplication cyst. Schwannoma was diagnosed in three cases and an osseous pseudotumor, a lipoma and a teratoma in the other three.

Table 3 Histopathological findings
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Four tumors were revealed to be malignant (19%): a mucinous adenocarcinoma in a tailgut cyst, a choroidal melanoma metastasis, a solid fibrotic tumor (hemangiopericytoma) and an eosinophil chordoma.

Literature search

In the 39 publications, the recorded characterics regarding number of patients, gender, age, histopathology, rate of malignancy, surgical approach, postoperative morbidity, follow-up, and local recurrence are presented in Table 4.

Table 4 Overview of literature
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Discussion

This study represents a single-institution series of retrorectal tumors and demonstrates a heterogeneity comparable to other reports and few systematic reviews [1,2,3,4, 9, 52, 53]. Its reported incidence ranges from 0.9 to 6.3 patients per year and is estimated as one in 40,000 hospital admissions [1, 3, 4, 52]. In our retrospective study, we report on 21 patients treated between 2002 and 2022.

Retrorectal tumors can be divided into five categories, congenital (55–65%) being the most common [1, 4, 6,7,8, 54]. As in our data the vast majority are benign and occur predominantly in females. Two of the four malignant tumors in our series, however, were found in male patients.

During embryologic development, a tail is formed from the endo-, meso-, and ectodermal tissues. If the tailgut does not recede, a remnant can result as a tailgut cyst [3, 6]. Resection is recommended because of the risk of malignant transformation [9, 55]. In our study, in accordance with published data [9, 55], benign tailgut cysts were the most common entity, while in one patient a poorly differentiated mucinous adenocarcinoma was found in the cyst. In another patient it remained unclear whether the lesion should be classified as a tailgut or duplication cyst.

The rate of malignancy is reported to range up to 26.6% [9, 56]. In 2022, Burke et al. described a malignancy rate of 17.3% in a large series of 144 tumors [16], which accords with our data. The highest rate of neoplasia of 26.6% was found in a systematic review comprising 196 patients [56].

The most frequent malignant retrorectal tumor is the chordoma, which results from persistence of endoderm, probably from residue of the chorda dorsalis [1, 8, 57]. In our study one patient presented with an eosinophilic chordoma.

With a frequency of 10-12%, neurogenic tumors are the second most common entity and are predominantly benign [4]. In various publications, schwannomas, in particular, have been described, as we found in our study (see Fig. 2) [1, 58].

Another 12–16% of retrorectal tumors are miscellaneous, often rare entities [3, 4, 7, 8]. In single patients, we found benign lesions (osseous pseudotumor, lipoma) as well as a malignant lesion with a solid fibrotic tumor (hemangiopericytoma), and a previously unreported metastasis of a choroidal melanoma.

The presentation can be nonspecific, even asymptomatic, and thus diagnosis is often incidental and at an advanced stage [1]. Indeed, the majority of our patients had nonspecific symptoms such as back and lower abdominal pain, and diagnosis was based on incidental findings in one quarter. Neurologic symptoms, such as the dorsiflexion of the foot seen in one, can also occur.

MRI and CT scans are considered the gold standard for evaluating these tumors beside the clinical examination. MRI can distinguish tissue properties and relations to neighboring organs [1, 6], often allowing accurate tumor diagnosis. In our series, 95.2% of the retrorectal tumors were confirmed or detected by MRI. CT allows clear visualization of bone structures and the differentiation between solid and cystic lesions [1, 6].

The use and value of biopsy remains controversial in current literature [1, 6, 12, 53]. Glasgow and Dietz refer to the risk of infection with subsequent sepsis, such as a biopsy of an anterior sacral meningocele leading to meningitis [8]. Additionally, the risk of biopsy-related tumor cell dissemination has to be considered. If tumor categorization is not possible and the option of neoadjuvant therapy must be considered, biopsy appears to be reasonable. In our study, in 47.6% of cases a biopsy was performed. It proved to be essential to therapeutic planning (radiation and immunotherapy) in the patient with the choroidal melanoma metastasis, our only patient not undergoing surgery.

Treatment depends on the tumor entity. In most cases - including asymptomatic tumors - a complete resection is indicated because of the potential for tumor growth with increasing symptoms and risk of malignant transformation [8, 52].

For surgical planning the location and size of the tumor and its relationship to neighbouring organs are relevant. Diagnostic and therapeutic algorithms have been proposed [11, 18, 32, 49]. Surgical options are posterior, anterior or combined approaches. As described by Dozois et al. [59, 60], a line through sacral vertebra three is helpful for decision-making. For small tumors below this line, the posterior approach may be sufficient, like that first described by Kraske in 1886 as the transcoccygeal approach for rectal cancer [8, 61]. This is the most common approach and was used In 70% of our patients. If the tumor is above the S3 line, the anterior, abdominal approach is advisable, although large tumors may require a combined approach. In 45% of our patients, a resection of bone structures (e.g. the os coccygis) became necessary to facilitate operative access or achieve complete tumor resection.

The postoperative complications in seven patients were Clavien-Dindo classification I in most (n = 4 (20%)) and were comparable to other studies [3, 13, 52]. In four patients a local recurrence was diagnosed. With no mortality, the resection of retrorectal tumors proved a predominantly safe procedure.

This study represents a comprehensive single-institution series of retrorectal tumors. The relatively small number of patients in this study likely may owe to the the rarity of retrorectal tumors. The retrospective design may affect accurate representation of the recurrence rate, however the represented rate of recurrence support the idea of a follow-up.

Conclusion

Retrorectal tumors are a heterogeneous entity. Our data show that most are benign. Resection is recommened and malignant entities may require multimodal therapy. In our cohort one patient had a very rare retrorectal metastasis of a choroidal melanoma, and another had a mucinous adenocarcinoma in a tailgut cyst. Biopsy may be helpful with inconclusive MRI findings and solid tumors. Decision-making by an interdisciplinary tumor board is recommended. The choice of surgical approach is determined by the tumor’s location and size. In our series, the posterior approach was most frequent.