Classification
Splenogonadal fusion is separated into two types:

Continuous (55%): The native spleen is connected to the gonad. The connection occurs through a cord of splenic tissue or fibrous band. Discontinuous (45%): Ectopic splenic tissue is present and attached to the gonad. An accessory spleen is present and the native spleen lacks the direct attachment to the gonad. Pathogenesis
The cause of splenogonadal fusion is still unclear, and there are several proposed mechanisms. A developmental field defect that occurs during blastogenesis is the current explanation of pathogenesis. The spleen derives from mesenchymal tissue and an inappropriate fusion can happen between the gonadal ridge during gut rotation, which occurs between weeks 5 and 8 of fetal life. Splenogonadal fusion may result from an unknown teratogenic insult. The timing of this insult may correlate to the severity of associated defects. There is also postulation that fusion may occur due to adhesion after an inflammatory response or a lack of apoptosis between the structures. Siblings documented to have splenogonadal fusion and an accessory spleen provides additional evidence of a possible genetic component. Associated Conditions
Additional congenital abnormalities are most often found associated with the continuous type of splenogonadal fusion. These abnormalities include micrognathia, macroglossia, anal atresia, and pulmonary hypoplasia. The most commonly associated malformation is cryptorchidism. When limb abnormalities occur, Splenogonadal Fusion with Limb Defects is made as a separate diagnosis. Splenogonadal Fusion with Limb Defects is also of unknown cause but some literature suggests that the condition may be related to Hanhart syndrome and facial femoral syndrome.
Caplans syndrome (or Caplan disease or rheumatoid pneumoconiosis) is a combination of rheumatoid arthritis (RA) and pneumoconiosis that manifests as intrapulmonary nodules, which appear homogeneous and well-defined on chest X-ray. Signs and symptoms
Caplan syndrome presents with cough and shortness of breath in conjunction with features of rheumatoid arthritis, such as painful joints and morning stiffness. Examination should reveal tender, swollen metacarpophalangeal joints and rheumatoid nodules; auscultation of the chest may reveal diffuse crackles that do not disappear on coughing or taking a deep breath. Caplan syndrome is a nodular condition of the lung occurring in dust-exposed persons with either a history of rheumatoid arthritis (RA) or who subsequently develop RA within the following 5–10 years. The nodules in the lung typically occur bilaterally and peripherally, on a background of simple coal workers pneumoconiosis. There are usually multiple nodules, varying in size from 0.5 to 5.0 cm. The nodules typically appear rapidly, often in only a few weeks. Nodules may grow, remain unchanged in size, resolve, or disappear and then reappear. They can cavitate, calcify, or develop air-fluid levels. Grossly, they can resemble a giant silicotic nodule. Histologically, they usually have a necrotic center surrounded by a zone of plasma cells and lymphocytes, and often with a peripheral inflammatory zone made of macrophages and neutrophils. Causes
Caplan syndrome occurs only in patients with both RA and pneumoconiosis related to mining dust (coal, asbestos, silica). The condition occurs in miners (especially those working in anthracite coal-mines), asbestosis, silicosis and other pneumoconioses.