Rice Body Formation Due to Different Etiologies in the Distal Forearm

Summary

The protocol describes the treatment of four rare cases of distal forearm synovitis with rice body formation from diverse etiologies (rheumatoid arthritis, trauma, and idiopathic) that were diagnosed by MRI and treated with surgical synovectomy and nerve release. No recurrence occurred postoperatively, underscoring surgery's efficacy in symptom resolution and prevention.

Abstract

Rice body formation in the distal forearm is an exceedingly rare clinical entity, often associated with chronic synovitis of varying etiologies. This study investigates four unique cases of forearm synovitis with rice body formation, hypothesizing that diverse underlying causes-rheumatoid arthritis, trauma, and idiopathic inflammation-contribute to this condition, and that surgical intervention ensures symptom resolution and prevents recurrence. The patients (three males, one female; aged 42-76 years) presented with heterogeneous clinical manifestations, including localized swelling, nerve compression symptoms, and restricted joint mobility. Diagnostic MRI revealed characteristic features: T1-weighted isointense masses with T2-weighted high-signal foci containing punctate low signals, aiding differentiation from other synovial pathologies. All patients underwent radical synovectomy with median nerve decompression, followed by histopathological analysis. Results demonstrated chronic granulomatous synovitis without evidence of infection (negative cultures and stains for tuberculosis, fungi, and bacteria). Postoperatively, all patients achieved complete symptom relief, with no recurrence or functional deficits observed during follow-up (9-22 months). Literature review highlighted the rarity of forearm rice bodies and underscored MRI's diagnostic superiority over radiography. The cases underscore that rice body formation, while historically linked to rheumatoid arthritis or tuberculosis, can arise from nonspecific synovial inflammation or trauma. Surgical excision combined with nerve release emerged as the definitive treatment, addressing both mechanical compression and inflammatory burden. This study emphasizes the importance of considering diverse etiologies in forearm synovitis, advocating for early MRI evaluation and tailored surgical management to optimize outcomes. The findings contribute to understanding the multifactorial pathogenesis of rice bodies and reinforce the efficacy of synovectomy in preventing recurrence and restoring function.

Introduction

Rice body is a kind of free particle with cartilaginous sheen, similar to the polished white rice, and was first reported by Reise in 1895 in a case of tuberculosis¹. It is mostly associated with rheumatoid diseases and tuberculosis^2,3, but it can also occur in trauma^4,5 or even in the absence of any clear cause^6,7. However, it is still very rare in the clinical practice of hand surgeons. Chronic nonspecific inflammation is thought to be associated with their formation, but the exact etiology and prognosis of rice bodies are still unknown.

Here we present four cases of rice body formation with chronic synovitis in the distal forearm, and a review of similar literature, focusing on the formation of rice body and discussing the diagnosis and treatment, with the aim of providing surgeons with ideas and theoretical bases for diagnosing and treating similar patients they encounter in clinical practice.

The rationale for developing and applying this technique arises from the diagnostic challenges and clinical consequences of rice body formation. Misdiagnosis or delayed diagnosis may prolong patient suffering, exacerbate nerve compression, and increase the risk of recurrence if incomplete excision is performed. By combining MRI-based early detection with definitive surgical excision and nerve release, this method addresses both the inflammatory burden and mechanical compression, thereby providing a comprehensive solution to optimize outcomes

The patients presented with localized swelling, nerve compression symptoms (e.g., numbness, positive Tinel's sign), and restricted joint mobility. Initial diagnostic tests included MRI, chosen for its superior soft-tissue resolution, which revealed characteristic rice body features: T1-weighted isointense masses with T2-weighted high-signal foci containing punctate low signals. These findings differentiated rice bodies from other synovial pathologies like pigmented villonodular synovitis (PVNS) or synovial osteochondromatosis, which exhibit distinct imaging patterns (e.g., hemosiderin deposition in PVNS or mineralization in osteochondromatosis). X-rays and CT scans were less sensitive but aided in assessing bony involvement and ruling out fractures. Laboratory tests-CRP, ESR, T-SPOT for tuberculosis, and bacterial/fungal cultures-were performed to exclude infectious or systemic inflammatory etiologies, all of which returned negative.

Compared with alternative imaging techniques such as radiography or CT, magnetic resonance imaging (MRI) provides superior soft-tissue resolution, enabling earlier and more accurate detection of rice bodies, as well as differentiation from mimicking conditions like pigmented villonodular synovitis (PVNS) and synovial osteochondromatosis^8,9. Previous studies have confirmed MRI's diagnostic superiority, as it identifies characteristic T1-isointense and T2-hypointense lesions with punctate hypointense foci, features that are often missed on X-rays or CT⁹. In terms of treatment, while arthroscopic debridement has been attempted, these methods are associated with incomplete clearance and higher recurrence rates¹⁰. In contrast, complete open synovectomy combined with nerve release has been consistently reported to achieve better symptom resolution, lower recurrence, and improved functional recovery. These advantages underscore why the present method is favored over less comprehensive alternatives.

The diagnosis of chronic synovitis with rice body formation was confirmed intraoperatively by histopathology, which demonstrated chronic granulomatous inflammation with lymphoplasmocytic infiltrates and necrosis, devoid of infectious agents or rheumatoid-specific features. Differential diagnoses considered included PVNS, synovial sarcoma, infectious tenosynovitis, and giant cell tumor of the tendon sheath, but MRI findings and histopathology excluded these.

The treatment plan involved radical synovectomy with median nerve decompression, aimed at removing inflammatory tissue, relieving nerve compression, and preventing recurrence. Surgical rationale centered on addressing mechanical compression (e.g., median nerve entrapment) and eliminating the inflammatory synovium responsible for rice body formation. Postoperatively, no recurrences or functional deficits were observed during follow-up (9-22 months), underscoring the efficacy of complete synovial excision. Potential complications, such as iatrogenic nerve injury, infection, or postoperative stiffness, were mitigated through meticulous surgical techniques and postoperative care. Long-term follow-up was emphasized to monitor for recurrence, particularly in idiopathic cases where the underlying etiology remained unclear. This approach highlights the importance of MRI in early diagnosis and tailored surgical intervention to optimize outcomes in this rare condition.

The primary goal of this method is to establish a standardized diagnostic and therapeutic approach that ensures early identification, accurate differentiation, and effective surgical management of rice body formation in the distal forearm. This method is most appropriate for clinicians managing patients with distal forearm swelling, nerve compression symptoms (such as numbness, tingling, or positive Tinel's sign), and restricted mobility where rice body formation is suspected. It is particularly valuable when initial radiographs or CT scans are inconclusive, but MRI demonstrates characteristic findings, and when laboratory studies exclude infectious causes such as tuberculosis or fungal tenosynovitis.

Protocol

The study protocols were approved by the Medical Ethics Committee of the First Affiliated Hospital of the College of Medicine, Zhejiang University. Written informed consent was obtained from the patients for publication of clinical details and clinical images.

1. Patient evaluation and initial assessment

1. Subject patients presenting with localized forearm swelling, numbness, restricted joint mobility, or positive Tinel's sign to a comprehensive clinical examination. Document symptoms suggestive of nerve compression or synovial pathology (e.g., progressive mass enlargement).
2. Obtain a detailed medical history, including prior trauma, rheumatoid arthritis, tuberculosis, or idiopathic inflammatory conditions. Medication use (e.g., immunosuppressants, corticosteroids) and record response to prior treatments.

2. Diagnostic imaging

1. Carry out a 3.0T MRI in a dedicated wrist coil with the forearm in neutral position. Carry out the following sequences: axial/coronal T1-weighted imaging (TR 500-700 ms, TE 10-20 ms, slice thickness 3 mm), fat-suppressed T2-weighted imaging (TR 3000-4000 ms, TE 50-80 ms). Key diagnostic criteria: rice bodies appear isointense to muscle on T1WI, hyperintense with punctate hypointense foci (salt-and-pepper sign) on T2WI, and demonstrate peripheral enhancement without central enhancement post-contrast. This protocol leveraged MRI's superior soft-tissue resolution to differentiate rice bodies from synovial osteochondromatosis or pigmented villonodular synovitis (PVNS).
2. Perform X-rays and CT scans to assess bony integrity, rule out fractures, or detect mineralization suggestive of alternative pathologies (e.g., synovial osteochondromatosis).

3. Laboratory testing

1. Carry out blood tests, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and rheumatoid factor (RF), to exclude systemic inflammation or autoimmune etiologies.
2. Perform T-SPOT testing, acid-fast staining, and fungal/bacterial cultures to rule out tuberculosis or infectious tenosynovitis.

4. Surgical intervention

1. Preoperative planning: Review MRI findings to delineate lesion margins and proximity to neurovascular structures. Map surgical access routes (e.g., longitudinal or S-shaped incisions) to minimize iatrogenic injury.
2. Perform all procedures under brachial plexus anesthesia with tourniquet control (250 mmHg) in a laminar-flow operating room. Prepare the surgical limb with sequential iodine-alcohol skin antisepsis 3x. Ask the surgical team to dress in full PPE (sterile gloves, fluid-resistant gowns, masks, and protective eyewear).
3. Administer a single preoperative 2 g intravenous cefazolin dose within 30 min prior to incision. Make a longitudinal/S-shaped incision along the volar forearm using a No. 15 scalpel blade, followed by sharp dissection through subcutaneous tissue with tissue scissors.
4. Using a No. 15 scalpel blade, an en bloc resection of the rice bodies together with the inflamed synovium was performed. Achieve hemostasis by bipolar cautery at 20 W setting (monopolar cautery avoided near nerves), and nerve decompression (if entrapped nerves) through longitudinal sharp dissection of the epineurium using microsurgical scissors - avoiding transverse traction to minimize postoperative scar constriction.
5. Rinse the wound surface with iodophor and clean water. After stopping the bleeding with an electric knife, perform layered suturing using 3-0 absorbable suture (Polyglactin). Apply 2 mL of sodium hyaluronate gel topically to reduce tendon adhesion. If tuberculosis or other communicable diseases cannot be ruled out, the surgical team wears N95 respirators, double gloves, and fluid-resistant aprons.
6. Send the synovial fragments and the contaminated liquid with blood for pathological examination, and then seal them in double-layer yellow medical waste bags¹¹.

5. Histopathological analysis

1. For resected specimens, carry out hematoxylin and eosin (H&E) staining to evaluate granulomatous inflammation, necrosis, and lymphoplasmocytic infiltrates.
2. Repeat with special stains (acid-fast, Grocott methenamine) and cultures on tissue samples to exclude occult infections.

6. Postoperative care

1. Avoid immediate postoperative immobilization to prevent tendon adhesion. Initiate early active mobilization protocols under physiotherapy guidance.
2. Administer analgesics (e.g., NSAIDs) and wound care to mitigate pain and infection risk.
3. The average hospital stay was approximately 1 week. Discharge patients once adequate pain control is achieved, the surgical wound is clean and stable, and early mobilization protocols can be initiated under outpatient supervision.

7. Follow up

1. Assess patients at 2 weeks, 3 months, and annually postoperatively. Carry out evaluations which include physical examination for recurrence, nerve function tests, and repeat MRI if symptoms recur.
2. Carry out long-term monitoring for early detection of recurrence, particularly in idiopathic cases, with a minimum follow-up duration of 12 months.

Results

Four cases were treated using the method described above. The details of all the cases and the outcome are described here.

Case 1

A 54-year-old woman presented to the hospital due to a 1-year history of a progressively enlarged mass in the distal left forearm. This mass was associated with numbness at the tip of the left fingers, but there were no signs of local infection and no restriction of wrist or finger mobility. The patient had no complaints of fever or joint pain, and the initial soybean-sized lump led to her neglect of treatment, so a year of medical records was unremarkable. She had a decade-long history of rheumatoid arthritis along with the consistent use of chewable calcium carbonate tablets, calcitriol, methylprednisolone, tripterygium wilfordii, and methotrexate to control the condition. She had no previous history of trauma or tuberculosis.

On physical examination, a soft, immobile mass (3cm x 4 cm) was found on the palmar surface of her wrist. The swelling had no tenderness, elevated skin temperature, or ulceration. But numbness in the fingertips and the positive Tinel's sign demonstrated the presence of localized nerve entrapment in her left hand. There was no joint pain, morning stiffness, or distal skin sensory abnormalities in her left upper limb, and the range of motion (ROM) of the wrist and fingers was normal.Laboratory test results, including white blood cell count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and T-SPOT test for tuberculosis infection, were normal. Magnetic resonance imaging (MRI) revealed an oval space-occupying lesion between the subcutaneous tissue and the tendons in the left medial forearm, with an intact capsule and well-defined margins. It appeared isointense on the T1-weighted image (T1WI) relative to muscle, while on the T2-weighted image (T2WI), it was a high signal foci with multiple punctate short signals. No significant intensity changes were seen in the center of the lesion after contrast injection, while the capsule was significantly enhanced (Figure 1). At the same time, a pulmonary radiograph was performed, and the results show no abnormalities.

Based on her medical history and examination findings, the patient was diagnosed with chronic synovitis, which may be caused by rheumatism, or a mass of synovial origin, such as giant cell tumor of the tendon sheath or synovial sarcoma. Considering its radiographic appearance and the potential for tissue rupture and limited joint motion associated with chronic synovitis^12,13, complete resection was the preferred option to be performed on this patient. After incision of the medial skin of the distal forearm, a well-defined, non-adherent, 4.5 cm x 3.5 cm x 1.0 cm, grayish-brown soft mass was visible, and it jammed against the median nerve, which might explain the patient's fingertip numbness and Tinel's sign. Thus, a section of the transverse carpal ligament and neurolysis of the median nerve were performed. After opening the protruded synovial membrane, we found the flexor tendon encircled by the thin tissue capsule, and there were numerous yellow, smooth rice bodies dispersed in the brown, clear liquid. All rice bodies were resected, and thorough excision of the dilated synovium was performed with respect to the neighboring neurovascular structures and the wrapped tendon (Figure 2).

The pathological findings of the specimen indicated that the mass was a fibrolipose connective tissue with multifocal granulomatous reaction, focal necrosis, and granulation tissue hyperplasia, and lymphocyte and plasma cell infiltrates were seen in the interstitium (Figure 3). There were no rheumatoid cells or Langerhans giant cells. Further tests performed on the tissue, including acid-fast staining, TB FISH, fungal FISH, general bacterial culture, Mycobacterium tuberculosis culture, and fungal culture, were all negative (Figure 4). The results indicated that the patient's synovitis did not meet the diagnostic criteria for tuberculosis or any other pathogen infection. Further PCR testing and rheumatoid-related specificity testing should be performed, but for economic reasons, the patient did not undergo those.

During 22 months of postoperative follow-up, the patient showed no signs of recurrence, and no motor or sensory dysfunction was seen in the distal forearm.

Case 2

A 70-year-old male had sustained multiple injuries to his right arm and right wrist in a car accident 1 year ago. After surgery, he gradually developed numbness in his right hand and right forearm and difficulty in the dorsal extension of his right wrist and metacarpophalangeal joint. He went to a local hospital for rehabilitation, but the condition did not improve. In the last 6 months, the patient's numbness and limited dorsiflexion in his right forearm got worse, but there was no pain or changes in temperature. He was so distressed by this that he came to the hospital. His past medical history was clean. Laboratory tests were also normal. X-rays of the hand reported only cortical grossness (Figure 5), and CT considered the presence of a fracture of the radius and extensive synovitis of the wrist with effusion (Figure 6). In the MRI, a large number of low-signal foci were found in the wrist lesion in the T2WI, while in the T1WI, there were only vague isosignal masses in the wrist, compared to the muscle. A synovectomy was performed, which revealed the presence of a large number of rice bodies, the largest of which was 1 cm in diameter. Neurolysis of the median nerve and open reduction and internal fixation of the fracture were also performed (Figure 7). Histologically, the synovium behaved similarly to case 1 (Figure 8). The patient's hand function returned about 3 months after surgery.

Case 3

A 76-year-old male presented with a sudden onset of swelling and pain in the 3rd and 4th fingers of the right hand 7 months ago, with limited finger flexion and dorsal extension, along with numbness in the fingertips, but no sensory discomfort. During this time, he received acupuncture and other treatments, but the symptoms continued to worsen, and then he developed atrophy of the thenar area in the right hand. He had no past history of rheumatoid or tuberculosis disease. Laboratory tests revealed no abnormal findings, even though multiple bacterial and fungal cultures of the exudate and TSPOT were performed. Electromyography (EMG) results showed the patient had severe carpal tunnel syndrome. MRI revealed an elliptical occupancy between the ulna and radius similar to that in cases 1 and 2. Clinically, we diagnosed it as carpal tunnel syndrome with soft tissue swelling to be investigated. Surgical exploration of the lesion was performed. In the medial forearm of the right hand, a yellow-white swelling was found to be lodged over the median nerve, from which rice bodies were gushing out; thus, we performed a wide synovectomy and median nerve release. Meanwhile, an incision into the patient's thenar area revealed the presence of a large amount of fluid, but no rice body was found (Figure 9). The final pathologic findings showed the same features as cases 1 and 2 (Figure 10). Further tissue culture and immunohistochemistry results proved to be negative. Postoperatively, the patient's hand symptoms resolved, and there were no signs of recurrence or hand function deficits at the 9-month follow-up visit.

Case 4

A 42-year-old male was examined with a 1-month history of a lump in his left wrist. The surface of the mass was intact, and there was no tenderness or elevated skin temperature. The patient did not exhibit numbness, sensory deficits, or decreased ROM of the hand. He declared two underlying conditions, dermatomyositis and hypertension, and fortunately, with medication control, his condition was stable. A past history of rheumatoid or tuberculosis disease was denied by the patient. The laboratory tests were normal. On imaging, a high signal elliptical lesion with multiple low signal manifestations within was found on T2WI of MRI, which had similar features as in cases 1-3. During surgery, we completely dissected a yellow-white mass of approximately 5 cm x 2 cm x 2 cm in size with multiple free mitochondria (Figure 11). Histologically, it showed soft tissue degeneration with non-acute inflammatory necrosis and cystic changes, without definite granuloma formation (Figure 12). After 14 months of follow-up, the patient had no signs of recurrence or tendon or nerve injury.

Summary of the outcomes

Following radical synovectomy with median nerve decompression, all four patients achieved complete resolution of symptoms, including localized swelling, nerve compression-related numbness, and restricted joint mobility. Postoperative evaluations at 9-22 months confirmed no recurrence of rice bodies or synovitis, as evidenced by clinical examination and follow-up MRI (Figure 1, Table 1). Intraoperative findings (Figure 2A-D) demonstrated successful en bloc resection of the inflammatory synovium and rice bodies, with histopathological analysis (Figure 3, Figure 4, Figure 8, Figure 10, Figure 12) confirming chronic granulomatous inflammation devoid of infectious agents or malignancy. Nerve decompression (Figure 2D, Figure 7F, Figure 9F) resolved Tinel's sign and restored sensory-motor function, with no postoperative complications such as infection or iatrogenic nerve injury. Imaging review (Table 2) highlighted MRI's diagnostic superiority in differentiating rice bodies from mimics like PVNS or synovial osteochondromatosis, while negative laboratory results (CRP, ESR, T-SPOT, cultures) excluded infectious etiologies. The article emphasizes meticulous synovectomy and early mobilization, aligned with literature reports of low recurrence rates (Table 2), underscoring its efficacy in addressing both mechanical compression and inflammatory burden. Long-term follow-up affirmed sustained functional recovery, supporting surgical intervention as the definitive treatment for distal forearm rice body formation.

Figure 1: MRI image of the left forearm. The morphology of the ulna and radius was normal; no obvious abnormal signal foci were seen in the bone. There was an elliptical abnormal signal foci in the medial left forearm between the subcutaneous and tendon space, with intact capsule and well-defined margins. Compared with muscle, it was isointense on (A, D) T1WI, while on (B, E) T2WI, a high signal focus with multiple punctate short signals. (C, F) After contrast injection, no significant intensity changes were seen in the center of the lesion, but the fibrous wall surrounding the rice body was significantly enhanced. The lesion grows along the subcutaneous muscle space, encircling the adjacent tendon. (A-C) Coronal-sectional images and (D-F) cross-sectional images. Please click here to view a larger version of this figure.

Figure 2: Intraoperative appearance of rice body and excision procedure. (A) A grayish-brown soft mass was pressing on the median nerve. (B) The lesion was opened to reveal the thin capsule of tissue encircling the flexor tendon, with numerous yellow, smooth rice bodies dispersed in the brown, clear liquid. (C) Removed rice body and capsule wall. (D) Structure of the distal forearm after removal of the lump. Please click here to view a larger version of this figure.

Figure 3: Microscopic structure of the H&E-stained specimen. The mass was a fibrolipose connective tissue with multifocal granulomatous reaction, focal necrosis, and granulation tissue hyperplasia, and lymphocyte and plasma cell infiltrates were seen in the interstitium. (A) At 50x magnification, (B) 100x magnification, (C) 200x magnification, (D) 400x magnification. Please click here to view a larger version of this figure.

Figure 4: Special staining of synovial tissue. (A) Acid-fast stain (negative), 400x magnification. (B) Grocott methenamine stain (negative), 400x magnification. (C) Mayer's stain (negative), 200x magnification. (D) PAS (negative), 200x magnification. Please click here to view a larger version of this figure.

Figure 5: X-ray of the right wrist. (A) Posteroanterior and (B) lateral radiographs of the right wrist joint. The distal cortices of the right ulna and radius were grossly cortical, and the remaining right carpal component bones are intact, with continuous cortical bone and blurred joint spaces. The wrist joint was in position, and the surrounding soft tissues were obviously swollen. Please click here to view a larger version of this figure.

Figure 6: CT imaging of the right wrist. (A) Coronal-sectional image and (B) 3D reconstruction image of CT of the right wrist. There was a tear fracture of the distal medial portion of the right radius with dislocation of the right wrist and swelling of the surrounding soft tissues. An old fracture of the right ulnar stem was considered. The bones of the right ulna and each bone of the right hand were osteoporotic and degenerated in the scan field. Please click here to view a larger version of this figure.

Figure 7: Intraoperative images of synovectomy and removal of rice bodies from the right wrist. (A) A S form of incision was made on the ulnar side of the right wrist, and after separating the subcutaneous tissue, a yellowish-white mass was visible. (B) Numerous rice granules were removed, and the largest one was 1 cm in diameter. Please click here to view a larger version of this figure.

Figure 8: Microscopic structure of the H&E-stained specimen. There was chronic granulomatous inflammation with necrosis at 100x magnification. Please click here to view a larger version of this figure.

Figure 9: Intraoperative images of synovectomy and removal of rice bodies from the right wrist. (A) Preoperative performance of the patient's right hand. (B) A longitudinal incision was made along the surface projection of the mass on the radial side of the right wrist, and after separating the subcutaneous tissue, a yellowish-white mass was visible. (C) The lump was lodged in the median nerve. (D) The rice bodies emerged from the mass. (E) Large fluid buildup can be seen when cutting through the large thenar area. (F) Complete resection of the synovium while protecting the surrounding tendons and vascular nerves. Please click here to view a larger version of this figure.

Figure 10: Microscopic structure of the H&E-stained specimen. There was an inflammatory capsule wall tissue with calcification and focal granulation tissue formation as seen here at 100x magnification. Please click here to view a larger version of this figure.

Figure 11: Intraoperative findings and removal of a rice body mass from the left wrist. (A) Preoperative performance of the patient's left hand. (B) A longitudinal incision was made along the surface projection of the mass on the radial side of the left wrist, and after separating the subcutaneous tissue, a yellowish-white mass was visible. (C) Large amounts of mashed potato-like substance (upper) and free rice bodies (lower) could be seen in the mass, which invaded the lateral joint capsule of the ulnar stalk (lower). (D) Complete dissection of the mass and suturing of the broken joint capsule. Please click here to view a larger version of this figure.

Figure 12: H&E-stained specimen. Microscopic structure of the H&E-stained specimen at 400x magnification. Please click here to view a larger version of this figure.

Case	Age/Sex	Previous history	Medical history	Symptom	Location in wrist	Immunological	Pathology	Treatment
1	54/F	Rheumatoid arthritis	1Y	S, N	Palmar, left	AFS(-), CRP(-),ESR(-),T-SPOT(-),fungus (FISH)(-)	G(+),N,LC	NMS+RS
2	70/M	Car accident injuries to the right arm and wrist	1Y	N, LA of right wrist and metacarpophalangeal joint	Palmar, right	RF(-),AFS(-), CRP(-),ESR(-),T-SPOT(-)	G(+),N	NMS+RS
3	76/M	Hypertension, leg fracture	7M	N, P, LA of right finger, atrophy of the thenar area in right hand	Palmar, right	RF(-),AFS(-), CRP(-),ESR(-),T-SPOT(-)	G(+),LC	NMS+RS
4	42/M	Hypertension, dermatomyositis	1M	S	Dorsal, left	RF(-),AFS(-), CRP(-),ESR(-),T-SPOT(-)	G(-), N	RS

Table 1: Clinical information of patients in the four cases. Abbreviations: Clinical information of patients in the present four cases, including demographics, medical history, clinical presentation, lesion location, immunological tests, pathological findings, and treatment details.F = female; M = male; Y = year; M = month; S = swelling; P = pain; LA = limited activities; RF = rheumatoid factor; AA = antinuclear antibodies; ESR = erythrocyte sedimentation rate; CRP = C-reactive protein; ZNS = Ziehl-Neelsen staining; AFS = acid fast staining; CSS = chronic non-specific synovitis; G = granulomatous; N = necrosis; LC = lymphoplasmocytic infiltration; NMS = neurolysis of median nerve; RS = radical synovectomy; NR = no recurrence.

Case[ref.]	Age/Sex	Medical history	Symptom	Location	Immunological	Pathology	Treatment	Follow-up
[1]	81/M	2Y	S	Left wrist; flexor synovial sheath	RF(-),	G(+),LC	Not reported	Not reported
					ZNS(-)
[2]	73/F	6M	S	Left  olecranon	RF(-)	LC	Bursectomy	20M, NR
[3]	61/F	6M	S, P	Right wrist, hand, and little finger; within flexor tendon synovial sheath	RF(-), ZNS(-), ESR(40 mm/ h), CRP(-)	LC	Tenosynovectomy	1M, NR
[4]	32/M	4M	S	Right wrist; within flexor tendon sheath	RF(-), AFS(-),  ESR(37 mm/ h)	G(-),LC	Surgical intervention	2Y, NR
[5]	68/M	1M	S, P, LA of right wrist	Right wrist; adjacent to the flexor tendons	RF(-), AFS(-), CRP(-),	G(+)	Surgical excision	4M, spontaneous rupture of the flexor tendons; 1Y, NR
[6]	51/M	2Y	S, P, numbness	Left wrist	AA(-), HLA-B27(-), AFS(-)	G(+)	RS	1Y, NR
[7]	62/M	3Y	S, P, decreased grip strength	Right wrist; within  synovial sacs	RF(-), ZNS(-), T-SPOT(-)	CSS	Wide synovectomy	2Y, NR

Table 2: Clinical characteristics and findings of patients with rice body formation of unknown etiology in the forearm. The table summarizes demographic features (age, sex), medical history, clinical symptoms, lesion location, immunological test results, pathological findings, treatment methods, and follow-up outcomes from representative case reports in the literature. Abbreviations: F = female; M = male; Y = year; M = month; S = swelling; P = pain; LA = limited activities; RF = rheumatoid factor; AA = antinuclear antibodies; ESR = erythrocyte sedimentation rate; CRP = C-reactive protein; ZNS = Ziehl-Neelsen staining; AFS = acid fast staining; CSS = chronic non-specific synovitis; G = granulomatous; N = necrosis; LC = lymphoplasmocytic infiltration; NMS = neurolysis of median nerve; RS = radical synovectomy; NR = no recurrence.

Discussion

Rice bodies are generally considered to be fibrin complexes resulting from inflammatory processes in the joint, and usually present as progressively enlarged masses⁶. Several hypotheses have speculated on its formation, but there is no consensus on its etiology.

The earliest one was the synovial origin hypothesis. Cheung et al. postulated that rice bodies were triggered by the microinfarcts of synovial cells that resulted from inflammation and ischemia. Subsequently, infarcted tissue is shed into joint fluid or bursa fluid and encapsulated by fibrin produced by synovial fluid¹⁴. Relevant microscopic observations are strong evidence for this hypothesis, such as the presence of microvessels and synovial-like protein components in the rice body¹⁵, vascular alterations (hyalinization, wall thickening, smooth muscle hyperplasia), iron-containing heme deposits, fat necrosis, and replacement of adipose tissue by collagen in some synovial villi^16,17, and the clinical findings that synovectomy prevented the formation of rice bodies in patients with rheumatoid arthritis and hyperplastic synovium¹⁸. After 2 years, however, Popert et al. found that the earliest rice bodies were predominantly fibrin in nature, and then they proposed the synovial fluid origin theory. According to it, the rice bodies were a new form in synovial fluid aggregated by fibrin-binding proteins and fibrin from scratch, independently of synovial debris². At the same time, a study of rice bodies induced by date puncture also found no type A, B, or C synovial cells, cartilage, or blood vessel formation in the rice body; instead, in that extra-articular site, it appeared that the rice body was composed primarily of fibrin¹⁹. Interestingly, rice bodies have also been found in pleural fluid²⁰, along the tendon sheath¹² and in the Bursa²¹, suggesting that this is of non-synovial origin and that rice bodies may have multiple origins depending on the site. In the present two cases, the rice bodies were found in the synovium of the medial forearm, and the molecular biology of the rice bodies has not been investigated, so our study is more supportive of a synovial-related origin, but the real etiology of each case is still debatable.

The greatest probability of occurrence of rice bodies is within the knee synovium or shoulder bursa of rheumatoid arthritis, where they are seen in 72% of patients with rheumatoid synovitis, regardless of the early and late stages of the disease², while in the forearm, to our knowledge, there are only three cases about this^12,22,23. This is often accompanied by pain and limitation of the joint motion. Given that the patient in the first case was a middle-aged woman with a 10-year history of rheumatoid arthritis in the past (Table 1), the possibility that the rice bodies were produced by rheumatoid synovitis should be considered. However, the patient did not present with the consistent clinical presentation of rheumatoid diseases, such as arthralgia or joint stiffness, and the ESR and CPR were within normal limits on laboratory tests. Besides the pathologic study suggesting granuloma formation was also inconsistent with the rice body caused by rheumatic disease, mostly without granuloma formation²¹. Unfortunately, the patient did not undergo subsequent testing for antinuclear antibodies and HLA B27. Generally, the clinical diagnosis of this patient with rice body formation due to rheumatoid arthritis is still under question, but it is probably the most likely reason. Since trauma or orthopedic manipulation also contributes to the formation of rice bodies, localization of the injury or around the implant is a common feature of them all. Pathologically, the mass shows chronic synovitis with or without granuloma formation^4,5. Therefore, in our opinion, the clear history of wrist trauma and pathological findings in case 2 strongly support the trauma as an etiology of rice body formation (Table 1). There are also many reports on the formation of rice bodies in extrapulmonary tuberculosis or atypical mycobacterium infection, such as tuberculous arthritis or tuberculous tenosynovitis. According to statistics, less than 50% of tuberculous tenosynovitis will occur, and there will also be pain and limited activity^3,24. The age and original nationality of all patients, as China is the country with the second-highest number of tuberculosis cases in the world, according to the WHO global tuberculosis report published in 2019²⁵, the formation of rice bodies caused by tuberculosis cannot be excluded. But their clean history of tuberculosis, lack of relevant symptoms, and completely negative laboratory results and immunological analysis deny this etiology (Table 1). The most powerful evidence, granuloma, as a pathological gold standard for the diagnosis of tuberculosis, is also not specific to tuberculosis infection. The final choice of PCR testing was also not performed for economic reasons. Therefore, clinically, none of the four patients could be diagnosed with mitochondrial formation due to tuberculosis. As shown in Table 2, nonspecific synovitis-induced rice body formation in the forearm occurs in patients with diverse and nonspecific clinical presentations, laboratory tests, and pathologic presentations did not support any of the causes we discussed above. The clinical manifestations closely resembled those observed in cases 3 and 4 (Table 1). Accordingly, the rice body formation in both cases was attributed to chronic synovitis of unknown origin.

While CT and X-ray images may be missing the representation of the mass, as shown in case 2, MRI is a preferred imaging modality for the diagnosis and detection of rice body, especially when it occurs within joints or in soft tissue spaces^26,27,28. MRI provides superior soft-tissue contrast resolution compared to radiography or CT, enabling detailed visualization of synovial structures, tendons, and neurovascular bundles without ionizing radiation²⁹. The rice body appears as an equal signal to the muscle on T1WI, and as multiple small and sparse bodies on T2WI. The typical size range is 2-5 mm. The size is relatively uniform, presenting as a low-signal-intensity mass distribution without enhancement, as shown in our case^6,30. This feature helps to distinguish it from pigmented villonodular synovitis (PVNS) and synovial osteochondromatosis. Synovial osteochondromatosis caused by metaplasia of the synovium is rich in cartilage when unmineralized and may produce loose bodies that are iso- or slightly high-intensity on T1WI and high-signal on T2WI compared to the low-signal skeletal muscle. It is a low-signal on both T1WI and T2WI after mineralization and is visible on both CT and X-rays³¹. PVNS, though similar to the clinical manifestation of rice body, usually shows signal void foci triggered by hemosiderosis, which is uncommon in rice body^32,33. In addition to helping to localize and diagnose the lesion, MRI also helps to determine the treatment plan by showing well-defined borders that provide the basis for complete surgical excision of the mass.

Unfortunately, ill-defined multiple rice body formations located in the distal forearm are very rare, and there is limited information regarding their treatment and prognosis. Early diagnosis and treatment can also prevent the continued progression of the mass that leads to its compression of the surrounding tissues, including nerve entrapment and tendon adhesion^34,35. Although surgery is used as a primary treatment option, we observed that Rice Bodies (RBs) occasionally disappeared during the follow-up period without surgical intervention³⁶. For cases with a small number, no symptoms, or mild symptoms, non-steroidal drug treatment can be given. For those with obvious symptoms, larger lesion volume, or an MRI indicating concurrent lesions, if conservative treatment is ineffective, arthroscopic debridement or synovectomy is recommended³⁶. In particular, these cases present obvious mechanical symptoms (such as joint stiffness, limited movement) or compression of the adjacent nerve and vascular structures by the synovial sac, along with an infection risk, and the imaging evidence provided by MRI. These factors led us to recommend that patients undergo a complete synovial resection to further analyze the cause and formulate a customized treatment plan.

It is noteworthy that three of our patients, whose mass was located on the palmar side of the wrist, showed signs of nerve compression, which is consistent with the intraoperative finding that the mass was located over the nerve and was jamming the median nerve³⁷. Therefore, in the case of a large synovial mass and rice body formation in the medial forearm, we should be alert to the possibility of nerve entrapment, even if the patient does not present with associated symptoms. Careful dissection of the mass and nerve release should be performed, taking care to avoid nerve damage during the procedure, which requires the surgeon's extensive surgical experience. Since the cause of the rice body could not be determined in these four patients, the standard clinical protocol for such cases is lacking; histological examination does not always reveal the exact cause of the disease, and there is a risk of misdiagnosis. It is recommended that the patients check in periodically to confirm the absence of recurrence.

This protocol underscores several critical steps, including preoperative MRI for precise lesion delineation, en bloc resection of rice bodies with inflamed synovium, and simultaneous nerve decompression to prevent recurrence and relieve compression. Modifications may be required in cases with extensive lesions, such as combined arthroscopic and open approaches, and troubleshooting strategies focus on careful neurovascular dissection, meticulous hemostasis, and adhesion prevention. Nonetheless, limitations remain, including the invasiveness of the procedure, possible diagnostic uncertainty despite MRI and histopathology, and the absence of standardized guidelines given the rarity of forearm rice bodies. Compared with arthroscopic debridement, which is associated with incomplete clearance and higher recurrence, this open synovectomy protocol provides more definitive outcomes by addressing both inflammatory and mechanical components. Looking forward, minimally invasive adaptations, intraoperative imaging guidance, and molecular characterization of rice bodies may refine the technique and broaden its applicability to other anatomical sites where rice body formation occurs.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3.0T MRI Scanner (Skyra)	Siemens Healthineers	Not specified
Acid-fast Stain Kit	Solarbio Life Sciences	G1170-50
bipolar electrotome	Wuhan Maolang Medical Technology Co., Ltd.	20162012293
Cefazolin (Injection, 2g)	Shijiazhuang No. 4 Pharmaceutical Co., Ltd.	H20054256
Grocott Methenamine Silver Stain Kit	Sigma-Aldrich	HT100A
Hematoxylin and Eosin Staining Kit	Beyotime Biotechnology	C0105S
Mayer’s Hematoxylin Stain Kit	Solarbio Life Sciences	G1120
PAS Stain Kit	Solarbio Life Sciences	G1281
Sodium Hyaluronate Gel (2ml)	Seikagaku Corporation Takahagi Plant	H20140533