The study, published in Frontiers in Marine Science, focused on four species with high market value in the Eastern Province of Saudi Arabia: the spangled emperor Lethrinus nebulosus, known locally as shari; the bludger Carangoides gymnostethus, known as deela; the pinkear emperor Lethrinus lentjan, known as bakhsheena; and the white-spotted spinefoot Siganus canaliculatus, known as safee. These species represent three families and are among the most prevalent commercial fish in Jubail Province. The researchers recorded the length and weight of every fish, inspected the body surface, fins, and head visually and by palpation, and carefully removed and measured any tissue masses for size, consistency, and cut surface characteristics.

Gross pathological examination revealed distinct patterns across the affected species. In the spangled emperor, a prominent swelling appeared in the dorsal-caudal region near the posterior end of the dorsal fin, and reflection of the skin exposed a well-circumscribed, round, white nodular mass measuring 20 millimeters in length and 15 millimeters in diameter. In the bludger, a similar swelling near the lateral line concealed a globular, lobulated, creamy-white mass with visible fine vasculature on its surface, measuring 25 by 20 millimeters. Notably, when the excised masses from both species were placed in a jar of water, they floated, a pathognomonic feature of high lipid content that immediately suggested a diagnosis of lipoma.

Histopathological assessment using hematoxylin and eosin and Masson’s trichrome stains confirmed that the growths in both the spangled emperor and the bludger were lipomas arising from the subdermal layer. The neoplastic tissue was composed mainly of proliferating fat cells, or adipocytes, that were well differentiated and contained large intracytoplasmic vacuoles displacing the nuclei to the cellular periphery. Some hyalinized skeletal muscle cells and fibrous connective tissue from the stratum compactum of the subcutaneous skin were observed between the proliferated adipocytes. The tumor masses showed no evidence of mitoses or other criteria of malignancy, and the presence of isolated muscle fibers between adipocytes likely represents entrapment of existing tissue during expansive tumor growth rather than true infiltration, distinguishing these cases from the infiltrative lipomas described in goldfish and farmed Mediterranean seabass.

A more unusual finding emerged in the pinkear emperor, where a solitary, fleshy, well-pedunculated overgrowth extended laterally on the left side near the posterior end of the dorsal fin in the caudal peduncle region. The lesion measured 15 by 10 millimeters, showed epidermal ulceration on its surface, and was firmly attached to the underlying musculature. Necropsy examination revealed no evidence of distant metastasis to other visceral organs. Histopathological examination showed masses of skeletal muscle underlying the ulcerated skin, with muscle fibers exhibiting a complete loss of the normal parallel arrangement of myotomes. The fibers were long and spindle-shaped with oval nuclei, forming irregular clusters cut transversely and longitudinally in a random fashion, with polygonal profiles within the tumor mass. Bony spines of the dorsal fin were observed in association with a marked increase in collagen fibers that stained positively with Masson’s trichrome. Loss of muscular striation and Zenker’s necrosis were not uncommon. Critically, the absence of pleomorphism, cellular atypia, and mitoses indicated no evidence of malignancy, leading to a diagnosis of rhabdomyoma, an exceptionally rare benign skeletal muscle tumor in marine fish from the Arabian Gulf.

The most aggressive lesion was found in the white-spotted spinefoot, where a large, fleshy, highly vascular mass measuring 55 by 20 millimeters was attached to deep muscle tissue around the vertebral column. The tumor expanded into the abdominal cavity, displacing visceral organs while remaining attached to the muscular tissue surrounding the spine. Despite this localized infiltration and significant size, gross examination revealed no further systemic involvement or evidence of metastasis. Histopathological investigation revealed a neoplastic overgrowth characterized by features of malignancy, including proliferation of poorly differentiated skeletal myocytes accompanied by inflammatory cell infiltration and hemorrhage. Zenker’s necrosis of the myocytes was not uncommon, and dystrophic calcification surrounding the neoplastic tissue was also observed. Multiple intracellular eosinophilic hyaline substances of various sizes within the tumor cells and macrophages were consistently noted, along with newly formed blood vessels, marked mitotic activity, frequent mitoses, and edema. The tumor cells exhibited clear pleomorphism, with significant variation in cell size and shape, nuclear atypia with enlarged hyperchromatic nuclei and prominent nucleoli, frequent atypical mitotic figures, and loss of the normal fascicular architecture typical of healthy muscle tissue. Based on these findings, the tumor was diagnosed as rhabdomyosarcoma, a malignant skeletal muscle neoplasm of probable myogenic origin.

The Arabian Gulf presents a uniquely stressful marine environment characterized by extreme salinity, fluctuating temperatures, and significant anthropogenic pressure from the oil and gas industry. It acts as a sink for various pollutants, including heavy metals, petroleum hydrocarbons, and polychlorinated biphenyls. During the Gulf War, approximately 11 million barrels of oil were released into the western coastal areas of the Arabian Gulf, forming oil slicks that extended more than 1,200 kilometers southwestward from Mina Al-Ahmadi to Qatar. Oil pollution has both short-term and long-term effects on fisheries production, potentially causing severe mortality of fish eggs and larvae and reducing larval hatching success. Industrial pollutants in the region, including PCBs and hydrocarbons, are known to interfere with cell signaling and DNA repair mechanisms, raising the possibility that environmental contamination could contribute to tumor formation in marine organisms.

However, the researchers urge considerable caution in interpreting these findings as indicators of environmental integrity. The low observed frequency of 0.54 percent, with a 95 percent confidence interval of 0.29 to 0.99 percent, might initially suggest a sporadic occurrence unlikely to result from severe pollution in the area. Species-related susceptibility, age-related factors, genetic predisposition, chronic tissue injury, spontaneous neoplasia, and infectious or viral factors are all considered relevant in fish tumorigenesis. Mesenchymal tumors, particularly rhabdomyosarcomas, have been experimentally induced in fish using chemical carcinogens such as N-methyl-N-nitrosourea, demonstrating that chemical exposure can indeed produce such lesions. Nevertheless, the diversity of tumor types in a single geographical region warrants concern and suggests these fish may serve as biological sentinels for the Gulf ecosystem.

Distinguishing between benign and malignant mesenchymal tumors is vital for assessing the impact on fish populations and for marketability considerations, as the unsightly appearance of such growths may affect consumer acceptance. The diagnostic challenges are considerable: differentiating true lipomas from reactive inflammatory fat necrosis or chronic granulomatous responses requires careful histological evaluation, while the rarity of rhabdomyomas necessitates exclusion of post-injury tissue repair and regenerative muscle hypertrophy. For rhabdomyosarcomas, the lack of validated species-specific immunohistochemical markers means diagnosis must rely strictly on hematoxylin and eosin morphology, with differential considerations including poorly differentiated fibrosarcoma and undifferentiated pleomorphic sarcoma.

The study provides a critical baseline for future surveillance of mesenchymal tumors in the Arabian Gulf and fills a significant gap in the marine pathology of the Saudi Arabian coast. Future studies should employ immunohistochemistry to further elucidate the histogenesis of poorly differentiated sarcomas, and correlating tumor prevalence with heavy metal concentrations in fish tissues will be a crucial next step in determining whether these neoplasms could act as biomarkers of environmental degradation. The researchers emphasize that the environmental link should be framed as a hypothesis and a rationale for future investigation rather than a confirmed conclusion, while continued histopathological surveillance remains essential for monitoring the health of the Gulf’s demersal and pelagic fish populations.

Subject of Research: Marine Biology

Article Title: Descriptive morpho pathological lesions and surveillance baseline of mesenchymal tumors in some commercially important marine fish species from the Arabian Gulf, Saudi Arabia

Article References: Al-Hizab, F. A., Al-Dhuayan, I. S., Mahmoud, M. A., & Ibrahim, M. M. (2026). Descriptive morpho pathological lesions and surveillance baseline of mesenchymal tumors in some commercially important marine fish species from the Arabian Gulf, Saudi Arabia. Frontiers in Marine Science, 13, Article 1972671. https://doi.org/10.3389/fmars.2026.1972671

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1972671

Keywords: fish tumors, Arabian Gulf, marine pathology, environmental toxicology, rhabdomyosarcoma, lipoma, fish health, Saudi Arabia, Descriptive, morpho, pathological, lesions

The research, led by Marianne Lappalainen of the Royal Veterinary College in London together with colleagues from referral centers across the United Kingdom, France, Belgium, Ireland, Switzerland, Spain, and Italy, took a retrospective approach. The team contacted veterinary oncology services across Europe and combed their medical records for dogs in which advanced imaging reviewed by a board-certified radiologist had been combined with cytological or histological confirmation of a primary intrapelvic lipoma. Crucially, the investigators excluded any mass that had merely spread into the pelvis from elsewhere, ensuring that every case represented a tumor that truly originated within the pelvic canal. Because the condition is so rare, the authors set no time limit on case selection, gathering examples across an open-ended window. Thirteen dogs made the final cut.

The affected dogs were, in keeping with what is known about lipomas in general, middle-aged to older animals. The median age at diagnosis was nine years and five months, with a range from roughly seven and a half to twelve years, and the median body weight was 24.45 kilograms. English Springer Spaniels topped the breed list with three of the thirteen cases, followed by crossbreeds and Labrador crosses; single cases appeared in Labrador Retrievers, Standard Poodles, English Cocker Spaniels, West Highland White Terriers, Golden Retrievers, and Smooth Collies. Interestingly, males slightly outnumbered females in this cohort, with a male-to-female ratio of four to three—a finding that runs counter to earlier UK primary-care studies suggesting that neutered females carry a higher risk of lipomas overall. The authors caution that the small sample size may explain the discrepancy.

The clinical picture was dominated by the bowel. Tenesmus—persistent, straining attempts to defecate—was recorded in nine of the thirteen dogs, or 69.2 percent. Altered stool shape, the classic signature of a mass compressing the colon and rectum into a narrowed channel, appeared in six dogs (46.15 percent), while dyschezia, painful or difficult defecation, affected four dogs (30.7 percent). Two dogs struggled to urinate, and one presented with constipation and vomiting. Remarkably, one lipoma was discovered incidentally during a routine rectal examination in a dog whose owners had noticed nothing wrong. For the rest, clinical signs had been present for a median of just twenty-one days before diagnosis, ranging from five to 180 days—a shorter interval than the seven and a half months reported in earlier work on benign and low-grade intrapelvic tumors, though individual dogs in this series did endure signs for up to six months.

Computed tomography emerged as the undisputed diagnostic hero of the study. Every dog underwent a CT scan, and in twelve of the thirteen cases (92.3 percent) the mass displayed the hallmark fat attenuation that essentially announces a lipoma on the scan. The thirteenth dog’s mass showed a mixture of fat and soft-tissue attenuation, yet histopathology subsequently confirmed it as adipose tissue all the same. In one case the CT report described the mass as infiltrative, a detail that would later prove prognostically important. On cross-sectional images, the tumors showed a striking positional preference: of the ten dogs in which the location was described, nine had lipomas on the left side of the pelvic canal, shoving the colon and rectum to the right. Where measurements permitted, the team calculated tumor volumes using the ellipsoid formula, finding a median volume of 161.2 cubic centimeters and dimensions ranging from about 5 by 3 by 5 centimeters in a Springer Spaniel to a remarkable 6 by 3 by 23 centimeters in a Labrador Retriever.

The imaging modality matters because the pelvic bones themselves conspire against simpler tools. Abdominal radiography and ultrasonography, the workhorses of general practice, struggle to visualize masses in this region because the surrounding bone obscures detail. Ultrasound can suggest a lipoma when it reveals an oval, well-defined, encapsulated mass with internal striations, hyperechogenicity, and a telltale absence of blood flow on color Doppler examination, while liposarcomas tend to appear heterogeneous with increased vascularity and invasion of nearby structures. But CT provides something neither can: precise information about a mass’s size, extent, and relationship to surrounding organs, which is indispensable for surgical planning. In human medicine, magnetic resonance imaging is often preferred for its superior soft-tissue contrast, but in veterinary oncology MRI remains rarely used for staging or surgical planning due to time and cost. The study’s findings suggest that for these patients, a CT scan alone can deliver a confident radiological diagnosis, potentially eliminating the need for preoperative cytohistopathology in some cases.

All thirteen dogs underwent surgery, via either a perineal approach in two cases or a caudal ventral celiotomy in seven; the surgical reports for four dogs were unavailable for review. No intraoperative complications were reported anywhere in the cohort, and the only perioperative problem was a single wound dehiscence two days after surgery, which was repaired without further incident. Pathology confirmed the benign nature of the tumors: all initial histopathology reports described well-differentiated adipocytes, the microscopic signature of a lipoma. Yet the very blandness of these tumors creates a diagnostic trap, because lipomas histologically resemble normal subcutaneous fat and often lack clear borders, making surgical margins difficult or impossible to evaluate. Margins went unreported in twelve of the dogs, a gap the authors attribute to the difficulty of distinguishing neoplastic from normal adipocytes, the benign expansile nature of the growths, or inadequate sampling.

The outcomes were largely encouraging, with one sobering caveat. Four dogs remain alive with a median follow-up of 507 days after diagnosis. Five dogs were euthanized, but only one of those deaths was attributed to the lipoma itself; the median time to death among the four with known dates was 889 days, ranging up to 1,740 days. Kaplan–Meier analysis, which accounts for the heavily censored data produced by long survival and lost follow-up, yielded an overall survival time of 1,020 days—nearly three years. The caveat concerns recurrence: three dogs (23.1 percent) experienced regrowth at a median of 220 days after their initial surgeries, a rate the authors note is uncomfortably close to figures reported for infiltrative lipomas, a more aggressive variant whose recurrence rates after excision range from 36 to 50 percent even with aggressive surgery. One recurrent case was confirmed histologically as an infiltrative lipoma, matching the earlier CT suspicion of infiltration.

Even more striking was the fate of one dog that recurred twice. Cytology at its third relapse suggested malignant transformation into a soft tissue sarcoma, and the dog was switched to metronomic chemotherapy—oral low-dose cyclophosphamide combined with the anti-inflammatory drug meloxicam. The authors weigh several explanations: an initial misdiagnosis, an original mixed tumor only partially characterized, or the development of sarcoma following repeated surgical injury, a phenomenon with tentative support in the literature linking tissue trauma to sarcoma formation. A fourth dog suspected of recurrence turned out to have intra-abdominal adhesions rather than tumor, though without necropsy the team could not definitively rule out regrowth. The episode underscores a broader point: not every returning symptom means the cancer is back.

For veterinary clinicians, the practical takeaways are concrete. A lipoma belongs on the differential diagnosis list for any intrapelvic mass in a dog, and CT imaging can reliably identify its fat content and map its relationship to the colon, rectum, and urinary tract. Surgical excision, though demanding specialized expertise that may exceed the capabilities of general practice, offers a favorable prognosis with low complication rates and survival approaching three years—provided owners and veterinarians remain vigilant for recurrence, particularly when the initial imaging hints at infiltrative behavior. The authors acknowledge the limits of their work: a small sample, retrospective design, referral-only population, and loss of follow-up in nearly a third of cases all constrain the statistics. Larger studies with longer follow-up, including cases of infiltrative lipoma, will be needed to refine the prognosis and clarify how different treatments shape outcomes. Until then, this rare and easily overlooked tumor has a documented playbook—and for most dogs, a genuinely good ending.

Subject of Research: Clinical presentation, CT diagnosis, surgical treatment, and outcomes of intrapelvic lipomas in dogs

Article Title: Presentation, treatment, and outcome of lipomas of the pelvic canal in dogs

Article References: Lappalainen, M., Gomez Fernandez, J., Béguin, J., Fournier, Q., Hayes, A., Bing, Y., Rodiño-Tilve, V., Bazelle, J., Borrego, J., & Desmas-Bazelle, I. (2025). Presentation, treatment, and outcome of lipomas of the pelvic canal in dogs. Veterinary Oncology, 2(1), Article 28. https://doi.org/10.1186/s44356-025-00044-1

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00044-1

Keywords: lipoma, dogs, pelvic canal, computed tomography, veterinary oncology, surgical excision, tenesmus, dyschezia, infiltrative lipoma, recurrence, Kaplan-Meier survival, case series