We present a 23-year-old woman with no previous relevant medical history, family history, or pre-existing condition, except for a history of cesarean sections. The patient presented with persistent left hypochondrial pain for 2 months, characterized by an insidious onset, a more-or-less stationary course, and a dull, aching nature. Clinical examination detected no abnormality apart from an ill-defined left hypochondrial swelling. Abdominal and pelvic post-contrast computed tomography (CT) described a large, well-defined left hypochondrial cystic lesion, measuring 19×18×13 cm (Fig. 1). The swelling was inseparable from the gastric fundus, with obliteration of fat planes adjacent to the spleen. The image was suggestive of a cystic gastrointestinal stromal tumor or a gastric duplication cyst. Endoscopic ultrasound (EUS) described a huge, well- defined, encapsulated perigastric mass lesion with heterogenous echogenicity and hypovascularity, approximately 14×7 cm in size. The mass was separated from the left liver lobe and in contact with the gastric wall. EUS biopsy indicated low-grade papillary proliferation. Tumor markers (carcinoembryonic antigen and CA 19-9) were within normal ranges. The patient was prepared for surgical resection, which was performed under general anesthesia, endotracheal intubation, and in a supine position. Exploration through an upper midline incision revealed a large mass originating from the left hemidiaphragm, separable from the spleen, left liver lobe, and stomach. Using monopolar electrocautery and a vessel sealing device (Ligasure; Medtronic, Minneapolis, MN, USA), transabdominal wide local excision of the mass was performed with a full-thickness resection of its diaphragmatic origin. The resection resulted in a large diaphragmatic defect that could not be primarily repaired (Fig. 2). The defect was reconstructed using a 15×15 cm double-layer mesh, secured to the diaphragmatic surface with polypropylene sutures. An intercostal tube was also inserted. The abdominal wound was closed over drains placed in the abdominal and subcutaneous layers. The patient was initially transferred to the intensive care unit for 24 hours and subsequently moved to the inpatient department. She was discharged after 11 days without any postoperative complications.

Figure 1. Post-contrast abdominal computed tomography (CT). Sagittal reconstruction (A) and axial (B, C) contrast-enhanced CT images demonstrate a large, mildly enhanced soft tissue mass in the left hypochondrium, measuring 18×14 cm (arrows). This mass appears inseparable from the left diaphragmatic copula. It contacts the gastric greater curvature and spleen without invasion. No intrathoracic extension or pathological regional lymph nodes.

Figure 2. An intraoperative photo. The photo shows the abdominal incision, left liver lobe, small intestinal lobes, and the diaphragmatic defect, as well as the lung base.

Gross examination of the mass revealed a large, well-circumscribed, encapsulated mass, measuring 22×17 cm, with an attached segment of muscle tissue (Fig. 3A). The mass had a firm, whitish, homogeneous cut surface with few foci of hemorrhage. Microscopic examination revealed spindle cell proliferation infiltrating the adjacent muscle bundles (Fig. 3B–D). This proliferation consisted of long sweeping fascicles of spindle cells with bland-looking nuclei and no evident atypia. Additionally, hypocellular areas, dense collagenized stroma, and thin-walled blood vessels with occasional stag-horn architecture were observed, along with areas of micro-hemorrhage and sporadic mast cells. No evident mitotic activity or necrosis was identified. Immunohistochemical (IHC) staining showed a positive nuclear reaction in tumor cells for β-catenin and a focal positive reaction for SMA, while S100, CD34, and desmin demonstrated negative reactions (Fig. 4). The safety margins were free of tumor tissue, leading to the diagnosis of fibromatosis.

Figure 3. Gross and microscopic examination of the tumor. (A) Gross image of the tumor with the attached muscular segment of the diaphragm. (B) Fibromatosis histopathology; spindle cell proliferation with infiltrative border and infiltrating the adjacent muscle (hematoxylin and eosin stain [H&E], ×40). (C) Cellular area showing fascicles of spindle cells with bland-looking nuclei and absent mitosis (H&E, ×100). (D) Hypocellular area showing collagenized stroma and thin-walled blood vessels with occasional stag-horn vessels (H&E, ×40).

Figure 4. Immunohistochemical staining. (A) Positive β-catenin nuclear expression in the tumor cells (immunohistochemistry stain, ×200). (B) Focal positive SMA expression in the tumor cells. Positive SMA expression in the normal muscle cells (immunohistochemistry stain, ×100). (C) Negative S100 expression in the tumor cells (immunohistochemistry stain, ×100). (D) Negative CD34 expression in the tumor cells. Positive CD34 expression in the endothelial cells of blood vessels (immunohistochemistry stain, ×100). (E) Negative desmin expression in the tumor cells. Positive desmin expression in the muscle bundles (immunohistochemistry stain, ×100).

The patient was referred to a medical oncology clinic for postoperative follow-up and management. The follow-up CT scan showed no signs of tumor recurrence.

All procedures performed in the study involving human participants followed the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This is a case report in which ethical-specific approval can be waived. The patient signed written consent for the surgical maneuvers for resection and reconstruction. The patient provided informed consent for the publication of the case report and accompanying images.

Primary tumors of the diaphragm are an extremely rare condition. The incidence of primary diaphragm tumors (PDTs) is lower than that of secondary diaphragm tumors that metastasize from lung cancer, mesothelial malignancies, thymic cancer, and liver cancer [1]. Desmoid fibromatosis, a type of PDT, is a rare soft tissue neoplasm that originates in musculoaponeurotic structures and predominately affects young adults between the ages of 20 and 40 years [2]. It is characterized by aggressive growth and local invasion but lacks metastatic potential [3]. The clinical course is unpredictable, and local recurrences are common [4]. The most commonly used imaging techniques for diagnosing desmoids are CT and magnetic resonance imaging [5].

Here, we report an exceedingly rare case of desmoid-type fibromatoses (DF) that was successfully resected, along with reconstruction of the diaphragm. This case represents only the third instance documented in the literature and is the first to involve a female patient. The findings from the 2 previously reported cases are summarized in Table 1 [6,7].

Table 1 . Comparison between the previously mentioned cases in the literature and the current one.

Case report	Suzuki H. et al (1992)	Peng Huang et al. (2022)	Current case
Sex	Male	Male	Female
Age (yr)	15	30	23
Presentation	Right hypochondrial mass	Abdominal mass	Left hypochondrial pain
Radiological findings	CT showed a mass in the medial region of the left lobe of the liver, the gallbladder was compressed dorsally, and a mass protruding into the thoracic cavity was observed on the cephalic side.	CT showed a mass of slightly low density shadowing the left diaphragmatic foot, with uneven density and unclear boundary. The lesion showed uneven progressive enhancement.	CT described a well-defined, large left hypochondrial cystic lesion. The swelling was inseparable from the gastric fundus, with obliteration of fat planes adjacent to the spleen.
Operative finding	A mass protruding from the diaphragm to the abdominal cavity with no adhesions. The tumor protruded into the thoracic cavity with no adhesions to the lungs.	The lesion was located at the foot of the left diaphragm.	Large mass originating from the left hemidiaphragm, separable from the spleen, left liver lobe, and stomach.
Management	The tumor was removed, and the diaphragm was excised. A part of the anterior chest wall containing the 7th to the 10th rib was also removed.	Excision of the tumor	Complete mass excision was performed with full-thickness resection of its diaphragmatic origin. Reconstruction of the defect with a 15×15 cm double-layer mesh. An intercostal tube was inserted as well.
Histology	Growth and bundle-like arrangement of spindle-shaped cells and collagen fibers.	The tumor was composed of hyperplastic spindle cells and collagen fibers, and the cells were arranged in bundles with infiltrative growth, without obvious atypia.	The tumor is bland-looking spindle cell proliferation dissecting the muscles, forming intersecting fascicles & areas of diffuse growth that are partially hypercellular with dense stroma & partially hypocellular with loose stroma. The composing cells are spindled with bland-looking nuclei & no significant atypia. There are intervening thick-walled blood vessels and scattered mast cells.
Immuno-histochemical staining	Not available	Not available	Positive for β-catenin and a focal positive reaction for SMA & CD 34, while desmin & S100 showed negative reactions.

CT, computed tomography..

Soft tissue tumors known as DF are extremely rare and originate from fibroblasts. The annual incidence of DF is roughly 0.0002%–0.0004%. This condition predominantly affects women and typically manifests between the ages of 15 and 60 years, though its cause remains unknown. Conversely, PDTs are exceedingly rare, with only a few cases documented in the literature. The first reported case occurred in Japan [6], involving a 15-year-old male with a right hypochondrial mass. Initially suspected to be a liver mass based on angiography, CT, and abdominal ultrasonography, its precise location and right-sided diaphragmatic origin were confirmed during laparotomy surgery. This procedure also revealed compression and protrusion into the liver. Histological analysis confirmed the diagnosis of fibromatosis, showing proliferation of collagen fibers and spindle cells arranged in a bundle-like pattern. The surgical intervention included the removal of a portion of the chest wall along with the tumor and the diaphragm. The second reported case involved a 30-year-old man with an abdominal tumor [7]. Imaging indicated that the left diaphragmatic foot was shadowed by a mass with uneven density and a hazy boundary with slightly low density. Uneven progressive enhancement was observed in the lesion. Post-surgical histological examination of the removed tumor revealed that it consisted of collagen fibers and hyperplastic spindle cells arranged in bundles, with infiltrative growth that showed no signs of atypia—leading to a diagnosis of fibromatosis.

The morbidity of benign and malignant diaphragm tumors is comparable. The most frequent solid tumors are lipomatous masses, while diaphragm cysts are the most common benign tumors. Furthermore, there have been isolated reports of pathologically benign or malignant soft-tissue tumors, including those of vascular, nerve sheath, smooth muscle, and fibroblastic/myofibroblastic origin. DF, in particular, originates from the diaphragm and may extend into the chest or abdominal cavities [6,8]. In this report, we describe a 23-year-old woman who initially presented with persistent left hypochondrial pain and was eventually diagnosed, via imaging and pathological examinations, with DF located in the left hemidiaphragm region.

It is important to differentiate this disease from the following conditions: (1) Solitary fibrous tumor: This uncommon spindle cell tumor is characterized by significant inhomogeneous enhancement. In addition to the invasion of neighboring organs, a marked difference from DF may be seen in the abundance of tortuous empty blood vessels within or surrounding the lesion. (2) Rhabdomyosarcoma: A mesenchymal cell-derived malignant tumor. It is generally markedly amplified, and metastases are possible. DF is classified as an intermediate tumor because, despite its invasive growth, distant metastasis is difficult to achieve. This characteristic helps to differentiate DF from primary soft tissue malignant tumors. Diaphragm DF is rare in clinical settings; although CT and magnetic resonance imaging are useful in identifying and localizing the disease, it remains challenging to differentiate it from a diaphragmatic malignant tumor. When diagnosing with imaging, the possibility of this condition should be considered [7]. In our case, the CT scan of the abdomen and pelvis suggested either a cystic gastrointestinal stromal tumor or a gastric duplication cyst. EUS described a large, well-defined, encapsulated perigastric mass lesion with heterogeneous echogenicity and hypovascularity. The diaphragmatic origin of the mass was confirmed only after surgical exploration.

Even after exploration, the diagnosis remains a challenge. An IHC investigation is ultimately necessary to confirm the diagnosis and rule out other possibilities [9]. In our case, β-catenin IHC labeling revealed a positive nuclear reaction in the tumor cells, along with a localized positive reaction for SMA, and negative reactions for S100, CD34, and desmin.

Treatment options for desmoid tumors include observation, surgery, radiation therapy, and systemic therapy with nonsteroidal anti-inflammatory drugs or targeted therapies such as imatinib. The choice of treatment depends on various factors, including tumor size, location, symptoms, and patient preferences. Surgery is often considered the primary treatment option for DF, with the goal of achieving complete resection. However, this is challenging due to the tumor’s infiltrative nature and proximity to vital structures. Radiation is frequently used when full resection of the tumor is not possible or when surgery is not feasible. Radiation can help manage tumor growth and alleviate symptoms. Tyrosine kinase inhibitors like imatinib have demonstrated encouraging outcomes in the treatment of fibromatosis, especially in individuals with β-catenin gene mutations. In our case, a large, well-circumscribed, encapsulated mass measuring approximately 22×17 cm was observed. A portion of muscular tissue was attached to it. The mass was completely removed, its diaphragmatic origin was fully resected, and the defect was repaired using a 15×15 cm double-layer mesh. Additionally, an intercostal tube was placed.

Primary DF is a very rare tumor, with only 2 cases previously reported in the literature. We describe a case involving a 23-year-old woman diagnosed with DF. She underwent surgical exploration, during which excision, full- thickness resection, and reconstruction of the defect using a double-layer mesh were performed. Histopathological analysis confirmed the diagnosis of fibromatosis; the tumor cells were positive for β-catenin and showed focal positivity for SMA, while testing negative for other antibodies. Despite its rarity, this diagnosis should be considered in cases involving primary diaphragmatic tumors.

Author contributions

Conceptualization: OH. Data collection: RA, RAA, RE, MT. Writing and revision: OH. Revision and editing: RA, RAA, RE, MT. Preparation and editing of the radiology part: GAS. Preparation and editing of the pathology part: SR. All authors have read and approved the manuscript.

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Funding

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

Acknowledgments

All the clinical, radiological & pathological data used in this manuscript are available on the Mansoura University medical system (Ibn Sina Hospital management system; http://srv137.mans.edu.eg/mus/newSystem/).