Thoracic Fetiform Teratoma: A Case Report of a Very Rare Entity in a Peruvian Hospital

Abstract

Mature fetiform teratoma, or homunculus, is a term coined for a rare variant of teratoma with a prevalence of 0.01% of teratomas. There have been very few cases reported in the world, and its thoracic presentation is extremely unusual. We present the case of a 31-year-old female patient with a history of progressive chest pain in the left hemithorax, associated with dyspnea on moderate exertion and cough. Imaging studies revealed a large intrathoracic tumor visually compatible with a teratoma. Surgical resection by a clamshell approach was successful, and subsequent anatomopathological studies of the operative specimen concluded that the mass was a mature fetiform thoracic teratoma. The treatment of this entity is generally surgical and includes wide resection due to its large adhesive component to surrounding tissues. Thus, the cardiothoracic surgeon must know approaches that allow wide resection, making these cases true surgical challenges.

Case report

This study was approved by the Institutional Review Board (IRB) of the Department of Thoracic and Cardiovascular Surgery, Edgardo Rebagliati Martins National Hospital (IRB approval no., 367-CTCV-10/22). The patient provided written informed consent for the publication of the research details and clinical images.

Mature fetiform teratoma or homunculus is a term coined for an extremely rare variant of teratoma that resembles a malformed fetus. Its incidence is presumed to be 0.01% and only 35 cases (1–65 years) have been reported worldwide to date [1]. Mature cystic teratomas are common benign formations that occur more frequently in women of reproductive age, and many of them are made up of mature, disorganized, and neoplastic tissues from the 3 embryonic layers [2]. In rare cases, these tumors achieve a high degree of differentiation and tissue organization, resembling a malformed fetus or homunculus. There are few reports associated with thoracic involvement (only 4 cases reported); however, when they do, they behave like a mediastinal tumor and could generate symptomatology by mass effect towards vital organs according to their progressive growth [1,2]. The treatment of thoracic mature fetiform teratoma is generally surgical and includes wide resection due to its large adhesive component to pericardial, pulmonary, and thoracic cage tissues; therefore, it is necessary for the cardiothoracic surgeon to have knowledge of approaches that allow wide resection such as standard, clamshell, or hemi-clamshell approaches, making these cases true surgical challenges.

A 31-year-old woman with no relevant medical history came to the emergency room with moderate exertional dyspnea (New York Heart Association class II) associated with oppressive chest pain, predominantly in the left hemithorax and a nonproductive cough that had lasted for 1 month. A physical examination revealed decreased vesicular murmur in the left hemithorax, and contrast-enhanced tomographic studies showed an extensive mass with well-defined borders (17×15×9 cm) and heterogeneous content, dependent on the mediastinum, and extending and causing compression of the entire left lung, with a mass effect on mediastinal vessels and heart. The presence of fat density, cystic areas, and gross calcifications was also noted (Fig. 1). A percutaneous anatomopathological study preliminarily revealed a mature thoracic teratoma and immediate surgical resection was indicated. The approach was by bilateral transsternal thoracotomy (clamshell incision). A wide incision was made from the anterior axillary line of the left fifth intercostal space to the contralateral side, sectioning the sternum and carefully dissecting the mediastinal planes (Fig. 2).

Fig. 1.

Triplanar thoracic tomography with contrast showing the intrathoracic tumor involving the left hemithorax (A–C). There is evidence of fat density, cystic areas, and thick calcifications within the tumor.

Fig. 2.

Surgical resection of fetiform thoracic mature thoracic teratoma. (A, B) A clamshell incision allowed greater exposure of the operative area and total tumor exeresis. (C, D) Operative specimen after resection, with fetiform morphologic characteristics.

A large tumor was found with adhesions to the wall, great vessels, pericardium, and lingula, for which the latter had to be resected by means of an atypical pulmonary segmentectomy along with the rest of the affected tissues. This resection of the tumor was performed with harmonic electrocautery, which allowed adequate control of hemostasis, due to the vascular collateral found during tumor dissection. The walls of the tumor were smooth, with areas of indurated and gelatinous consistency, with a regular vascular pattern. Adherent to and within the cyst was found a fetiform structure, covered with a viscous, yellowish, sebaceous substance. The structure had a cephalic pole, a central trunk, and outlines of upper and lower extremities, covered with dermal tissue, fine and long hairs, in the cephalic portion, and the rest covered with fine lanugo (Fig. 3). After surgical resection and without any associated complications, the left lung recovered its capacity and expansion, and finally, the patient was discharged in an asymptomatic condition and was scheduled for an ambulatory check-up visit 15 days after surgery.

Fig. 3.

Pathological study of the operative specimen. (A, B) Tissue corresponding to the skin, hair follicles, sebaceous glands, eccrine ducts, bronchial epithelium, hyaline cartilage and peribronchial seromucous glands with smooth and striated muscle tissue, adipose tissue, mature peripheral nervous tissue with nerve ganglion cells, thymus, bone, and bone marrow.

The postoperative anatomopathological evaluation revealed a surgical specimen weighing 1,450 g, corresponding to dense fibroconnective and adipose tissue with chronic inflammation and isolated venous vascular structures. The tumor components were constituted by histological elements corresponding to the skin, hair follicles, sebaceous glands, eccrine ducts, bronchial epithelium, hyaline cartilage, and peribronchial seromucous glands with smooth and striated muscle tissue, adipose tissue, and mature peripheral nervous tissue with nerve ganglion cells, thymus, bone, and bone marrow. No central nervous tissue, spinal cord, or visceral organ structures were identified. The anatomopathological evaluation concluded, both on microscopy and macroscopy, that it corresponded to a mature fetiform teratoma.

Discussion

The anterior mediastinum is the most frequent site of occurrence of extragonadal germ cell neoplasms [3], constituting 15% to 20% of tumors of this compartment, and of these 70% are mature teratomas, which make up 3% to 13% of all anterior mediastinal tumors [4]. The highest incidence of this condition is in the third and fourth decade of life, with a mean age of around 30 years. It affects both sexes equally, although authors such as Fuentes Valdés [3] found a predominance of the female sex. These tumors are considered “giant” when they occupy half or more of a hemithorax, as in our case. Since the discovery of mature cystic teratoma, also called a dermoid cyst, researchers have been extremely interested in discovering its pathogenicity given its capacity to replicate any tissue of the human body [5]. These tumors are composed of mature, disorganized, but histologically differentiated tissues, originating from 1 or more germ layers (ectoderm, mesoderm, or endoderm) and with the potential to develop into mature or malignant tissue. On rare occasions, the tissues included in the tumor present a high degree of differentiation and organization that resembles a malformed fetus (fetiform structure), taking the name of fetiform teratoma, also called “homunculus”; this condition is very rare, with few cases reported in the literature [1,6]. Its main differential diagnosis is the fetus-in-fetu, which is a malformed, parasitic, diamniotic, monozygotic, diamniotic twin found inside the body of a living child or, sometimes, in an adult [7].

Regarding their pathogenesis, it is believed that mature teratomas arise from the parthenogenetic development of a single primordial germ cell that has completed the first meiotic division, since studies have determined that they are always homozygous, unlike normal tissues, which are heterozygous [1,6]. However, in a further analysis of fetiform teratomas, Miura et al. [7] demonstrated their origin from a mature ovum after the completion of meiosis II, with complete homozygosity at all loci. In comparison, fetus-in-fetu has its origin in an unequal division of totipotent cells of a blastocyst, with the inclusion of these cells in the more mature embryo, apparently due to a persistent anastomosis of the vitelline circulation during development [7].

Classically, both entities have been distinguished in that fetus-in-fetu requires for its diagnosis the presence of a developed and segmented axial skeleton; the presence of organogenesis has also been mentioned as a distinctive point, although characteristically fetus-in-fetu almost always presents with acardia and anencephaly [1]. In a study by Brand et al. [8], 91% of fetus-in-fetu were reported to have a spine, 82.5% extremities, 55.8% a central nervous system (always anencephalic), 45% a gastrointestinal tract, 40% vessels and 26.5% a genitourinary tract. This distinction turns out to be somewhat arbitrary, but it is supported by the fact that the presence of an axial skeleton indicates development beyond the primitive streak stage, which is considered highly developed for a teratoma. However, authors such as Kuno et al. [5] have reported fetiform teratomas with highly developed axial skeleton and organs that included a brain, eye, trachea, thyroid, blood vessels, intestines, and a structure similar to a male reproductive organ containing spongy vascular tissue. Surprisingly, there have been no reports of skeletal muscle tissue in homunculi, suggesting the possibility that paternal genetic information is required for their morphogenesis [5,6]. Something very curious in our case is that, despite the absence of an axial skeleton, central nervous tissue, and visceral organic structures, which inclines the diagnosis to a fetiform teratoma, we found a great variety of tissues, including striated muscle tissue.

There is a wide variety of forms of presentation and tissues present in both entities, which often share many characteristics in common, and there are even reports of the presence of simultaneous fetus-in-fetu and teratomas [9]. This prompted us to think that the morphological structure alone is not enough for their differentiation, which instead necessitates a cytogenetic examination based on zygosity. Teratomas are homozygous, unlike the heterozygosity of their host, but fetus-in-fetu is genetically similar to its host [6,9]. In our case, cytogenetic studies were not performed.

Nonetheless, a clinical differentiation can also be made: fetus-in-fetu is discovered mainly in childhood as an abdominal mass and it is unlikely for it to persist until adulthood; furthermore, the retroperitoneum is the most frequent location; although they can be found in atypical locations such as the skull, scrotum, sacrum, mouth, and adrenal gland [8]. In contrast, fetiform teratoma is most commonly seen in women of reproductive age and is mostly discovered as an ovarian mass; locations such as the thorax, as in our case, are much rarer. When fetiform teratoma arises in the ovaries, it must also be differentiated from ectopic pregnancy, distinguished by the absence of trophoblastic or placental tissue and no elevation of β-human chorionic gonadotropin [6,9].

Surgical treatment is the treatment of choice with good results. The surgical access must be adapted to the extension and size of the tumor to guarantee a safe dissection [1,4]; in our case, we decided to perform a clamshell incision due to the size and location of the tumor. In general, the prognosis of fetiform teratoma is favorable. During the postoperative period, complications associated with the size of the resected tumor have been reported in 15% of cases, such as effusion (24%), pyothorax (11%), collapsed lung (5%), or postcardiotomy syndrome (up to 2%); however, in our case, no associated complication was noted [3-5]. Nonetheless, it has been reported that up to 2% of mature cystic teratomas are malignant and about 10% of them recur after resection. Therefore, complete resection is recommended, along with surveillance comprising serologic and imaging tests [9]. Although the prognosis of fetus-in-fetu is more favorable, the presence of immature elements requires close follow-up [8].

A fetiform teratoma is a rare form of mature cystic teratoma with a high degree of tissue organization and differentiation, which makes it resemble a fetus. The degree of development can vary, which can make it difficult to distinguish from a fetus-in-fetu, especially in the less developed forms; therefore, its diagnosis requires an adequate clinical history and a thorough anatomopathological examination, with a cytogenetic study being useful, especially in difficult cases.

Funding Statement

Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.