New phenotype of accessory scrotum with perineal lipoblastoma: Coexistence of midperineal and lateral accessory scrotums


Yutaka Kanamori MD 7-3-1 Hong Bukyo-ku, Tokyo 113-8655, JAPAN. Email:


Abstract  We present the extremely rare phenotype of an accessory scrotum with an associated lipoblastoma. There was a coexistence of midperineal and lateral types. To our knowledge, this phenotype has never been reported. The lipoblastoma, which arose in the perineum, divided the moving labioscrotal swelling into three parts during early fetal life. This resulted in the specific anomaly in this patient.


Congenital scrotal anomalies are classified into four types: bifid scrotum, penoscrotal transposition, ectopic scrotum, and accessory scrotum.1 These anomalies are not common and accessory scrotum in particular is quite rare,2 with approximately 30 cases reported.1,3–5 The etiology of accessory scrotum is not clear but several hypotheses about its development have been proposed.1,6–8

In this report, we present an extremely rare phenotype of accessory scrotum with associated lipoblastoma and coexistence of midperineal and lateral accessory scrotums. To our knowledge this phenotype has never been reported before. This case may be important in the speculation of the etiology of accessory scrotum. We propose that the lipoblastoma arising in the perineum divided the moving labioscrotal swelling into three parts in early fetal life, resulting in the specific anomaly in the patient in the present report.

Case Report

A 9-day-old boy was referred to the Department of Pediatric Surgery at the University of Tokyo Hospital for the treatment of perineal anomalies. The patient was born at 39 weeks of gestation and his body weight was 3208 g. His general condition was well and he was recognized to have perineal abnormalities (Fig. 1). The line of raphe was curved to right side, and seemed to be oppressed by a subcutaneous mass located at the left sided perineal area. The size of mass was about 3 cm in diameter (Fig. 1), had a smooth surface and was soft in palpation. Furthermore, there were two abnormal skin protrusions, which were rugged, pigmented and resembled the skin of the scrotum (Fig. 1). One skin protrusion was sited on the raphe and another lesion originated at the left edge of the mass previously described. A protrusion on the raphe is usually called a midperineal type of accessory scrotum and the other one called a lateral type. To our knowledge, this is the first case where both the midperineal and lateral types of accessory scrotum have coexisted in one patient. The patient had no other anomalies at all, including any anorectal anomalies. He underwent surgical resection of both the subcutaneous mass and the two skin protrusions when 9 days-old and the post operative course was uneventful. The histological diagnosis of the subcutaneous mass was lipoblastoma, because most of the tumor composed of mature fatty cells (Fig. 2-a), but there were some lipoblasts among the mature fatty cells (Fig. 2-b). The two skin lesions were diagnosed as accessory scrotums because skin pigmentation existed and smooth muscle was seen at the subcutaneous area, which was considered to be equivalent to the dartos fascia of the normal scrotum.

Figure 1.

The appearance of the patient's perineal region. The raphe curves to the right side and seems to be oppressed by the mass sited at the left perineum. The mass is 3 cm in diameter and has a soft, smooth surface (arrrow heads indicate the edge of the mass). Two skin protrusions with pigmentation and wrinkling are present and the appearance resembles scrotal skin. One lesion is sited on the raphe and another is on the left edge of the mass.

Figure 2.

Microscopic findings of the mass lesion, which was diagnosed as lipoblastoma (HE). Lower magnification: most of the tumor is composed of mature fatty cells, as seen in lipomas of adults. Higher magnification: there are some lipoblasts among the mature fatty cells, which is in accordance with the diagnosis of lipoblastoma.


The case presented here is a new phenotype of accessory scrotum, in that both midperineal and lateral types coexisted on one patient with perineal lipoblastoma.

Scrotal development is closely related to penile development. At the fourth week of gestation, the phallus  develops abruptly and forms the penis, while at the same time, genital swellings appear at both sides of the inguinal region and gradually move to the posterior site and form the labioscrotal swellings at 10–12 weeks gestation. This swelling migrates further to the caudal area of the penile site and forms the right and left parts of the scrotum. Accessory scrotum can be expected to be caused if abnormal development of the labioscrotal swelling occurs in the early stage of fetal life.

There are some hypotheses about the etiology of accessory scrotum. Lamm et al. proposed that the movement of the caudal portion of the labioscrotal swelling to the midportion failed, forming the accessory scrotum.6 Noguchi et al. proposed another theory: that at the early stage of development, abnormal division in labioscrotal swelling may cause the accessory scrotum.7 By this theory, three divisions would result in the midperineal type of accessory scrotum, whereas two divisions of the right or left labioscrotal swelling would result in the lateral type. Takayasu et al. proposed that a teratoid growth of the pluripotential anlage of the labioscrotal swelling was responsible for the accessory scrotum.8 In addition, a recent report by Sule et al. speculated that the accessory labioscrotal fold usually develops because a perineal lipoma arising at the perineum disrupts the continuity of developing caudal labioscrotal swellings.1 The hypotheses of both Lamm et al. and Takayasu et al. do not fully explain the etiology of the lipoma in the present case, which was closely associated with the accessory scrotum. The theory presented by Noguchi et al. does not explain the present case because the midperineal and lateral types of accessory scrotum cannot coexist by their theory. However, the case can be explained by Sule's theory, because the developing lipoma divides the left labioscrotal swelling into three parts and the two caudal parts form the accessory scrotum; one is moved to the lateral side and the other one is forced to move to the midportion and is finally sited on the raphe.

The perineal mass in the present report was diagnosed as lipoblastoma because parts of the tumor were composed of lipoblasts. In addition, one paper has reported a perineal mass lesion seen in a neonate as lipoblastoma.9 However, these tumors are considered to be benign lesions and the prognosis is reasonably good.